1) I think the increase in probability of suicides is non-tiny

What would be the mechanism linking this post to future suicides? (See also below.)

2) I don’t value “not having taboos” particularly highly

That would certainly help to explain your reaction. I, however, value it very highly indeed, and think that taboos are incompatible with rationality and "enlightenment" values (such as freedom of speech) more generally. (There could be exceptions, but they must always be considered, and never knee-jerk or uncritically inherited from general society.)

3) I think there are better ways to express regret than by saying, essentially, “So did he do the right thing or what?”

You have misunderstood the post. It does not ask whether Chris did the right thing. It invites readers to consider the rationality of suicide in general. It also invites them to critically examine society's attitude (of which you evidently happen to be an exponent). It does so as a tribute to Chris: this is a discussion that I think he would have wanted to see happen, and I feel he deserves to have his fellow aspiring rationalists pay some attention to this issue before he is forgotten.

If you somehow found out that someone had decided to kill themselves because of this thread, how confident would you be that they made the right decision?

So far as I am aware, my post does not contain any argument in favor of any particular person committing suicide. It is therefore difficult to imagine that anyone could rationally decide to kill themselves "because of" it. And I do not accept the Orwellian idea that we can (or should) prevent irrational suicides by avoiding discussion of the issue. Even if the effect were non-negligible (which I don't particularly believe), I would not consider it worth the censorship cost.

In short, while I may very well say "Oh shit" in response to such a suicide, the significance of that exclamation would not be any different than if the person had committed suicide in response to any other LW post I had written (on any other topic).