IMDb forums is the gift that keep on giving.

 Take a look here.

According to some IMDb posters  Selma isn't registering well, audience rating wise, because of racism and a fictitious thing called a "liberal agenda." Here's what they had to say:

The average IMDb is a middle-class white fanboy who doesn't care about social issues and resents any film that steals the thunder from the latest Nolan geekfest, hence their hatred towards Selma. Many of them are also right-of-centre and possibly resent the coverage of the police killings of black men and see Selma as part of some 'liberal agenda' to make them face up to their own privileges.

and (by poster zombieDANCE)

 I laugh because this is probably true.

and (by poster ibaaaaaad)

Racists always troll the black-centric movies without seeing them. Not worth reading into.

I doubt many have heard of this movie, Selma, so allegations for middle white class down voting it is rather ridiculous. 
 
Now it's interesting that both poster zombieDANCE and ibaaaaaad are homosexuals. The zombie guy practically talks in cliches (the guy's is indignant beyond belief) and ibaaaaad is a Muslim, if I'm not mistaken, who isn't as pathetic as zombieDANCE but still has his moments of "well that's just racist!" And he doesn't like the late President Reagan because of how he handled AIDS.Well, if your fellow "love is love"/You-just-help-who-you-fall-in-love-with" peeps wouldn't part take in anal sex and carpet eating (though not a way of getting AIDS, but still) you wouldn't have such a big problem with this horrible disease. Go figure.

"But I lo - "
"It ain't love."