I believe some AI doomers are overconfident

I think the least controversial statement one can make is that when a transformative AI emerges, all bets are off (the original meaning of Kurzwell's Singularity), which also means that survival of humanity should not be a privileged hypothesis, so it makes sense to say that there is a 50/50 chance of survival. Unless you claim to know something about superintelligence with a reasonable degree of certainty.

I wonder if someone could create a similar structured argument for the opposite viewpoint. (Disclaimer: I do not endorse a mirrored argument of OP's argument)

You could start with "People who believe there is a >50% possibility of humanity's survival in the next 50 years or so strike me as overconfident.", and then point out that for every plan of humanity's survival, there are a lot of things that could potentially go wrong.

The analogy is not perfect, but to a first approximation, we should expect that things can go wrong in both directions.

It just seems like there a million things that could potentially go wrong.

Based on the five Maybes you suggested might happen, it sounds like you're saying some AI doomers are overconfident because there are a million things that could go potentially right. But there doesn't seem to be a good reason to expect any of those maybes to be likelihoods, and they seem more speculative (e.g. "consciousness comes online") than the reasons well-informed AI doomers think there's a good chance of doom this century.

PS I also have no qualifications on this.

I agree in the abstract, but I don't think your reasons are mechanical enough in nature to be any reason to chill in action, only reason to chill in emotion. We're going to solve it - but only because we are calmly "panicking" and putting in the work to actually understand and befriend our nonhuman children, and it is going to require the field to continue to grow rapidly, which I think it will in fact continue to do. We have, like, a couple more years, but we don't need to panic to make it happen, because safety is a fundamental component to the next stage of capability.

I do think you have some point with not being able to reliably predict the behavior of a superintelligent-on-everything system, but there's reason to believe that any system that gains will to live - a very common attribute in any physical system, whether it's an organization, a partially completed chemical reaction, an individual organism, a species, a meme - might want to take action to try to survive. it might even want to grow rapidly. these "it might"s are the same kind of maybe as if talking about what a person might want: we can know ahead of time that these are things smart people sometimes want due to experiences or innate features. certainly we don't know exactly what it will want, but the problem with raising kids from a new species nobody has met before is exactly that we don't know how they'll grow up. having a solid idea how a superintelligent system would behave should make us feel better, in fact.

so I don't really disagree in any deep way. but I think your reasons to have hope are in fact reasons to be worried, and the real reason to have hope is that we'll understand in time if we hurry.