I think it comes down to you shouldn't treat your opinion as if it is the only valid one.
So, state "Twilight is garbage" all you want (though those be fightin' words in these here parts ), but don't say, "Of course Twilight is garbage! "
But your opinion is the only valid one for *you*. You can be respectful to someone and fervently believe that Twilight is garbage and nothing anyone else posts or says will change that opinion.
Poster A: I love Twilight, it's the best!
Poster B: Not for me, Twilight is garbage.
Poster A: Ah, well I love Twilight and nothing will change that.
Poster B: I think its' garbage and nothing will change that.
Each one's argument is entirely valid only for themselves and the other person's opinion really doesn't need to mean anything or factor in. I've never ever understood why someone else's personal opinion of something matters at *all* in how you form your own.
I love plenty of things other people don't, but if they intensely hate something or think its fluff, I'm secure enough in my opinion that it doesn't matter to me at all. Why on earth should the fact that Susie hates Twilight, have any bearing at all on my opinion of it? It seems pretty self-centered to immediately think someone else's opinion of something was directly formed or has some direct link to your own.
Why can't people just like what they like and dislike what they dislike and leave it at that?