In this instance wouldn't 'preceding poster' be more correct than 'last poster'? ;)

Something something argument!

You failed to provide an explicit argument!

Meta-rant about how HN discussions fail to stick to the original topic

Right. I call it the Hacker News Right-Side Effect (or should that be Rule, like the Off Side one ... :):

In many HN threads with lots of comments, at some point in the thread (and very often starting at or near the top), the comments successively veer off to the right, sometimes to a ridiculous extent, forcing rightmost comments into a thin vertical column that is a pain to read. And worse, the main topic of the OP is often not discussed much at all, since the majority of comments are about these minute inconsequential details, as you say above - and since these trivia subthreads tend to get upvoted the most.

It's even worse when the thread veers into something political. You can write a 5 paragraph essay about some topic and someone will eventually come out of the woodwork to point out: "On paragraph 4, in this statement, you generalized and said 'all' and I can find a counterexample. Aha! You should have said 'many'! Your entire point is therefore invalid!!" Pedantic nitpicking is just part of this culture.

My favourite fallacy of all is the fallacy fallacy: whereby it is a fallacy of an argument to reject another argument if it contains or is composed of a fallacy. (https://en.wikipedia.org/wiki/Argument_from_fallacy)

It's why grammar nazis are the most insufferable, because their picking apart of your sentences appears to invalidate your argument, when really they're just being pricks.