*Epistemic status: I noticed a commonality between a set of rhetorical moves that I sometimes find irritating and sometimes think is valid.*

You claim P? OK. But even if you’re right about P…

- … if I assume P, then I can prove not P. So, by contradiction, P is false. So you’re wrong.
- … if you really believed P, then you would have a certain appropriate mood. But it doesn’t seem like you have that mood. So you’re wrong.
- … with 99% probability, as long as there’s a 1% chance that P is wrong, according to expected value, we should act like P is wrong. So you’re wrong.
- … accepting P would mean that you should do this weird action A. But you don’t do A, as far as I can tell. So you’re wrong.
- … yesterday, you said Q, and Q implies not P. So you were wrong yesterday or today. So you’re wrong.
- … somebody might infer Q from P. But Q is false! So you’re wrong.
- … someone might infer from your expression of P that you believe Q. But Q is false! So you’re wrong.

You're not wrong. This post wasn't really meant literally.

Speaking in the language of the post:

Well, look. Let's put to the side whether or not sin^2x + cos^2x is actually 1 or not. In today's culture, the obvious and natural interpretation of what you said is that sin^2x - cos^2x = 0. But that's a damaging belief for the future engineers of America to have, that could seriously harm their faith in the math education they received at our upstanding public schools, and so it's irresponsible for you to go around saying "sin^2x + cos^2x = 1" without clarifying exactly what you do or don't mean.

I hear your concern for our future engineers! They should have the best educational opportunities we can offer them, and I'm not it! Fortunately, I have no plans to go into teaching. Rather, I thought that the context of the discussion up to that point was sufficient to make clear what I meant by "sin^2x + cos^2x = 1", and not imply anything "= 0" that doesn't. Unfortunately, I've noticed the conversation drifting from the point I was trying to make (which I was making an effort to support). I meant to be addressing...

I sort of want to try developing (the valid version of) this into a deliberate skill. I think that of all the mundane forms of hypocrisy, one of the most vexing might be inconsistency at the 24h+ timescale. It's just hard to say, "hey, you're trying to have it both ways!" if the violation in question is spread out over multiple days. So naturally, everyone does it all the time.

The first bullet point seems valid(for propositions with no empirical content)

Indeed! The post would be boring if none of the bullet points were legit.