Not sure I agree with "most of the time", but anyway, isn't my friend's critique of ideas somewhat similar to my enemy's invective-filled ad hominem attack? Don't these all fall within perfectly ok behavior between adults who have chosen to spend time reading each others' thoughts?

I don't think so at all. Civilized debate over ideas? Great. Middle-school-tier name-calling, shaming tactics, and attempts to get someone fired from their job because you disagree with them? Completely unacceptable. Are we all in middle school now because we don't have to look at each other face to face?