Let's use a simple test based on common sense: how often do you see a human being solve problems requiring the use of reason when they're unconscious? Yes, you can find instances of geniuses like Ramanujan solving complex problem during or after a dream state, but those involve partial consciousness. You don't see guys like Einstein coming up with the theory of relativity while in a coma; the Founding Fathers didn't write the Declaration of Independence while sleep-walking; in fact, you can't even find instances of housewives putting together their shopping list for the week during deep delta-wave sleep. This is predicated on a hard definition of intelligence, requiring the use of reason; no one says, "That fly is intelligent" or "that squirrel is intelligent" precisely because neither is capable of using reason. This is a very high bar for A.I., but it is the common sense definition used by ordinary people as a matter of practicality, in everyday speech. Likewise, in practice, everyone assumes consciousness is necessary to the exercise of that kind of intelligence.
Conversely, we can come up with another common-sense based criterion for judging objections to this argument, particularly the solipsist one, based on 3 elements: 1) practicality; 2) the effect the objections have on those who hold them sincerely; and 3) the effect that actions based on those beliefs have on others. It's going to take me several paragraphs to make this case, but the length is necessary if I want to make the case in a complete, thorough fashion. It is true that we cannot prove that another human being possesses consciousness, if our standard is absolute proof. We cannot, in fact, provide absolute proof for anything; there's always room for some objection, no matter how ridiculous or trifling. As some philosophers have pointed out, perhaps all of reality as we know it is just a dream, or the product of some long, involved conspiracy like the plot of the Jim Carrey movie The Truman Show. The key to meeting such objections is that they require an infinite regress of increasingly untenable objections, whose likelihood plunges with each additional step required to justify such unreasonable doubts; I've always wondered if we could come up with a "Ridiculousness Metric" for Machine Learning based on the cardinality of such objections (or the pickiness of fuzzy sets). If we were to allow critics to stick their foot in the door with all manner of unreasonable objections, it would be impossible to close any debate. The human race would be paralyzed in inaction because nothing would be decidable; but as the rock band Rush once pointed out, "If you choose not to decide, you still have made a choice." At some point we must apply a test to decide such things, even in the absence of absolute proof; refusal to apply a test also constitutes a choice. Settling an argument of this kind is like a game of the Chinese game Go - once the other player's surrounded and has no more moves left to make, the game is over; if a person's evidence has debunked and they have no further justifications left, then we can conclude that they're acting unreasonably. There are people running around claiming the Holocaust never happened, or the Flat Earth Society, etc., but their existence shouldn't and doesn't stop us from taking action contrary to their ideas. We can debunk the objections of cranks like the Flat Earth Society beyond a reasonable doubt because in the end, they simply can't answer all of our rebuttals. I’m glad that qualia and Philosophical Zombies were brought up because they make for interesting conversation and food for thought, but solipsism is acted upon as rarely as the ideas of the Flat Earth Society precisely because the incomplete evidence we do have runs against it.
As G.K. Chesterton (a.k.a. "The Apostle of Common Sense") points out in his classic Orthodoxy, radical doubt of the kind many classical philosophers preached is not a path to wisdom but to madness; once we go beyond a reasonable doubt, we end up acting unreasonably. He says that in the absence of absolute proof we can fall back on another secondary form of evidence: whether a person's philosophy leads a man to Hanwell, the infamous British mental institution. Chesterton makes a good case that when people actually act on ideas like solipsism (rather than merely debating them in a pedantic manner in an ivy-covered classroom) they go mad The Philosophical Zombie argument is close to solipsism, which is actually one of the diagnostic criteria for certain forms of schizophrenia. The dehumanization that occurs when radical doubt is applied to qualia is also intimately tied in with sociopathic behavior, Although GKC does not cite his scary example directly, Rene Descartes was himself living proof. He was a brilliant mathematician who is still cheered for doubting all except his own existence, with the famous maxim "I think, therefore I am." But Descartes also used to carry a mannequin of his dead sister with him to European cafes, where he could be seen chatting with it. The gist of all this is that we can judge the worth of an idea by how it affects the well-being of the believer, or by how they in turn affect others through ethical choices based on those beliefs. When people actually act on radical doubt of the kind expressed in solipsism and denial of common qualia, it often has a bad effect on them and others they come in contact with.
In a roundabout way, the A.I. community also faces a quite serious risk - perhaps a permanent temptation - towards making the opposite mistake, of ascribing common qualia, consciousness and the like to its Machine Learning products without adequate proof. I recently heard a case made on shockingly bad logical grounds by well-respected academics to the effect that plants possess "intelligence," based on really weak definitions and clear confusion with self-organization. We cannot provide absolute proof that a rock doesn't have intelligence, which amounts to the old problem of disproving a negative. Thankfully, few men actually act on such beliefs at present, because when they do, they end up losing their minds. If we take such arguments seriously, we might see laws passed to protect the kind of Pet Rocks that were popular in the '70s (I'm still upset that mine was stolen LOL). It would be a lot easier, however, to make the same mistake of ascribing consciousness, intelligence and other such qualities to a state-of-the-art machine, because of wishful thinking, hubris, the lofty credentials of the inventors, the influence of science fiction and the modern love affair with technology. In the future, I have little doubt that we'll have Cargo Cult of A.I. - perhaps legally protected like some kind of endangered species, with civil rights, but having no more consciousness, soul or actual intelligence than a rock. Don't quote me on this, but I believe Rod Serling once wrote a story to this effect.
The best way to avoid this fate is to stick to the common sense interpretations and definitions of these things, which we keep backing away from in large part because they set a very high bar for A.I. that we may never be able to surpass in our lifetimes, if ever. Perhaps A.I. isn't even logically possible, at any level of technology; I recall a few proofs that can be interpreted to that effect. Those high but reasonable standards may be increasingly difficult to stick to if Chesterton and colleagues like Hilaire Belloc and Arnold Lunn were correct in their assessment that the use of reason has actually been breaking down in Western civilization, at least as far back as the Enlightenment; Lunn's 1931 book The Flight from Reason is a classic in this regard and has yet to be rebutted. This historical trend is a broad topic in and of itself - but suffice it to say that the denial of reason and obsession with technology are both directly relevant in obvious ways to the field of A.I. If the Flight from Reason is still under way, then we will be increasingly tempted to resort to feckless, facile objections in order to demote the use of reason and indispensable qualities like consciousness in our definitions of A.I., but come up with increasingly weak criteria for proving it; simultaneously, our technology will continue to improve, thereby boosting the "Artificial" side of Artificial Intelligence.
Don't get me wrong: if I didn't think we can do some really exciting things with A.I., I wouldn't be here. But most of them can be achieved without ever replicating actual human intelligence, by solving whole classes of tangential problems that are difficult for humans to think about, but which do not require consciousness or the use of reason that marks human intelligence. The image recognition capabilities of convolutional neural nets are one example, for instance; if we want human intelligence, we can always manufacture it through the easiest, most economical and time-tested way, by having babies. Perhaps these tangential forms of A.I. should be enough for us for now. We cannot inject the use of reason into our machines if we do not possess enough of it ourselves to decide whether reason is necessary for A.I., or even to discern what it consists of. We can't engineer or deprecate consciousness for A.I. till we're conscious of its significance. I'd wager, however, that everyone reading this thread and weighing intelligent responses is doing so in a conscious state. That in and of itself ought to answer our question satisfactorily for now.