There's a difference between giving advice from a position of authority and exploring the subject from a variety of angles. It feels to me as though you're accusing folks doing the latter of engaging in the former. Playing around with an idea and throwing out possibilities--some of them foolish or ill-advised, certainly--is at the core of the hacker culture, and I'd like to discourage you from criticizing people for doing so, while still maintaining your healthy skepticism.
I've often been known to comment on legal matters on HN, but I always steer clear of giving legal advice. (At least I hope I've never slipped up and done so.) And, as you well know, that's the proper course for anyone, regardless of whether they're a lawyer or not.
So just to echo and build on jsprinkles' various comments: It's OK to discuss the law in a general sense. I.e. you can talk about how things work, without giving an opinion as to the case at hand. But it's irresponsible and generally illegal to advise an individual on how s/he should proceed.
Example of a comment that's OK: "Trademark disputes often depend in part on the likelihood of consumers being confused by the respective marks."
Example of a comment that's not OK: "Trademark disputes often depend in part on the likelihood of consumers being confused by the respective marks. Since the OP's mark isn't going to confuse anyone, the plaintiff will probably lose."
I think that it's not as much that you're advocating for common sense, but that you're being really aggressive about it. Everyone can read and understand your point of view. Not everyone has to agree with it. You don't have a moral or ethical obligation to argue with people until they realize that you're right. Reasonable people can disagree, and on the internet, the standard of "reasonable" is often pretty low.
I personally agree with you in that I would never discuss pending legal matters with an online community. It seems too risky.
It also saddens me, as a tech-geek and business-geek and law-geek that we can't have transparent and "hackerly" discussions of these kinds of conflicts and possible ideas (not exactly full-on advice) for addressing and/or preventing them.
This advice transcends my allegiance, which is to nobody involved in this discussion (and which doesn't matter at all, frankly), and I'm annoyed that you think I'm stupid enough to involve myself in something I'm personally vested in.