Remaining anonymous given the political sensitivity of this issue, but I honestly don't see the problem. The point of a seminar is to improve a paper and to convince an audience - that is, to advance science. We all know how to read, so a seminar is not just about one way information flow.
As noted, a private conversation about a paper with a friend is much more two sided, with many challenging questions. I have never been to a seminar which came close to covering the issues the crowd was actually skeptical about, and everyone has seen the "talk seems to go well but in the elevator back, turns out everyone hated the paper because X, Y, Z.". As a *speaker*, I want as much feedback as possible - I already know what it is the paper!
Of course rudeness is not acceptable. But, if anything, I quibble with the audience members who, out of a desire for social niceties, do not actually contribute to improving the paper or diving deeper into points related to their area of expertise. We are trying to do science, not be therapists.