It's customary in some contexts to italicize "loan words". The terms for the fallacies come from the Latin. Ergo...
As for your second point, I think it's pretty clear from both my comments and their context why I'm pointing out those fallacies. That said, in the case of "non sequitur", I was actually referring more to the literary sense of the term — "Where the hell did that come from?" — than the fallacious "does not follow" sense.
Those terms are used all the time on hn but not usually italicized, but that's fair, I get your point.
When you respond twice in a row in a comment chain saying that they are using a logical fallacy, and nothing else, you've done nothing to add to the conversation, but are playing the role of Logic Studies 101 Professor. That's probably what they meant by the looking back on on your writing comment.
How often would a random selection of 1000 people from the 300 million be expected to intersect with the 10,000?
There are billions of facebook users, so this should be happening all the time by pure chance. But of course it's not pure chance. Facebook will be selecting from a pool much much smaller than 300 million, and the selections won't be random.