Normally once games come out, threads like these change into pro-character threads, for people who enjoy that character.
Back with Origins, you had the Zevran thread and the Alistair Gush Thread (as well as other threads, but those were my main ones), and for the most part, we tried to keep those threads positive. It was considered bad form to go into someone else's thread and bash the character, even though it happened. Other threads were started for those who didn't like the character, as a place for those people to vent. You can see that starting here -- I've seen both a pro-Vivianne thread and a dislike-Vivianne thread.
Some crossover discussion is good. A little debate can get you thinking about the character, help crystallize your thoughts. But discussion doesn't mean "anti". It makes it harder for people to come here and enjoy the character, with anti posts.
Just like on places like tumblr, it's nicer if the the pro and anti are separated. I'm sure there are other people who are anti-Blackwall/Rainer, and would help the venting process much more.