Gala -- have you checked out the politics category lately? Rife with disagreement -- healthy or no.
I really am very sympathetic to the idea of being passionate about literature. I am, too. The John Gray thing came up because I was a member of a book group from which I expected big things -- discussion of modern fiction in literary terms. Instead we read "Men are from Mars, Women are from Venus", which my husband hated vicariously because I kept stopping every few paragraphs and yelling, "This is totally WRONG! And what's not WRONG is lifted wholesale from Deborah Tannen, MINUS credit, of course. This guy is an IDIOT!" Then when we got together, everyone was talking about how great it was, blah blah blah, and I sat there jiggling my foot and biting my tongue.
But here's what I did. (I don't recall hating a book as much as that one before or since -- usually if it has the potential to unleash that kind of bile, I don't finish it or get wind of it ahead of time and don't bother with it at all.) I listened. I saw that people liked it. I took ahold of the points I agreed with. I had my copy of Deborah Tannen's "You Just Don't Understand" with me, and offered to lend it out. I read passages from Tannen. People listened to me back, were interested in what I had to say, and ended up saying "Jeez, that Gray fella's an idiot..."
If I had opened with "Gray's an idiot", after everyone had said how much they loved him, it would have been needlessly confrontational. A thoughtful discussion about gender roles, communication et al wouldn't have followed. And I got to say what I thought -- I wasn't lying, I wasn't misrepresenting -- I was just using a little bit of tact.
When I talk about generalized insults, I don't necessarily mean insulting the person -- I mean "he's a hack" or "he sucks" rather than the SPECIFICS. Specifics can be discussed; generalized insults don't further discussion.
Anyway, as dlowan said, I thought you were looking for suggestions. If not, that's cool.