What you say may be true for some, but in general from my experience, at least in the The Western Cultures, it is the idea of "The Rules of Debate", which place us in the position of adversaries. The conversation turns from "sharing" what we do to live and how we have learned to live, and letting others in on our personal perspectives to "fencing", where there can only be winners, losers and judges. Hubris becomes our armor and passive aggressiveness, overt aggression, character smearing, and ballistic ad hominem our dueling weapons.Spiny: I think generally people are just stating their opinions on a question of Buddhist ethics. I wonder if the perception of "lecturing" occurs when others don't like those opinions?
Ironically, none of us are morally superior when it comes to surviving by ingesting nutrients. We each for our karmic benefit or detriment have an obligation to understand and decide what to consume for the sake of our samsaric survival and decide which form of karmic consequences to accept as a consequence of doing so. Of course we can choose to starve as others have already pointed out. Not my path, though. "Me Tarzan! You Jain?"