I realise that I said "I'll just make a few points and leave it" and then, er, failed to do so. And lo, this looks like it could be the beginning of a lengthy discussion of evil and theism, for which LW probably really isn't the best venue. So I'm going to ignore all the object-level issues aside from giving a couple of clarifications (see below) and make the following meta-point:

You seem to be basically agreeing with my arguments and conceding that your counterproposals are shaky and speculative; my point isn't to declare victory nor to suggest you should be abandoning theism immediately :-) but just that I think this indicates that you agree with me that whether or not the world turns out to be somehow the best that omnipotence coupled with perfect wisdom and goodness can achieve, it doesn't look much like it is. In which case I don't think you can credibly make an argument of the form "the world is well explained by the hypothesis that it's a morally-optimal world, which is a nice simple hypothesis, so we should consider that highly probable". I've argued before that it's not so simple a hypothesis, but it's also a really terrible explanation for the world we actually see.

The promised clarifications: 1. The reason why my cancer-zapping proposal didn't involve curing all diseases was that it's easier to see that a change is a clear improvement if it's reasonably small and simple. Curing all diseases is a really big leap, it probably makes a huge difference to typical lifespans and hence to all kinds of other things in society, it probably would get noticed which, for good or ill, could make a big difference to people's ideas about science and gods and whatnot. I would in fact expect the overall effect to be substantially more positive than that of just zapping incipient cancers, but it's more complicated and therefore less clear. I'm not trying to describe an optimal world, merely one that's clearly better than this one. 2. My point about habits and advertising and the like wasn't that if free will matters then those things should have no effect, still less that it's a mystery why we have them; but that if our world is being optimized by a superbeing who values free will so much that, e.g., Hitler's free will matters more than the murder of six million Jews, then we should expect much less impairment of our free will than we actually seem to have.