From what I figure, it's this: people who have been lambasting everything Snyder makes, or even him as an individual, verified or not, already hate this movie and their opinions will not change once they see it because if the movie turns out better than they expect, it would require some humility which I don't think most of these people have. Some critics will be a part of this, but not all of them.
On the other side of the spectrum, you have people who already think it will be an epic superhero classic, and act toxic towards those who aren't on board. *cough* Snyder cultists *cough*
And then you have the middle folk who are interested in seeing it, fans of Snyder's stuff or not, and want to discuss things in a civil and constructive manner.
Bottom line is, bias will run rampant amongst many folk on social media in regards to this movie and it will be vitriolic and ugly as all hell. Avoiding Twitter when it premieres would be a phenominally good idea. Regardless of people's consensus, what matter is what you as an individual think of the film and whether you enjoyed it or not. That's my philosophy.