It’s not anonymity but the distance that matters. Plenty of people on Facebook with their real names, locations (through photos and events) don’t seem to care about saying things that they may not say face to face.
I think there are consequences, and I think the problem is jerks favor the punch in the gut over lukewarm ignorance they receive in return for little honest contributions. It's probably a natural tendency of a "superflat" social environment that hateful low-effort remarks pays off better.
The other problem I see is that a person says what they feel in the moment---and then they move on. But the (emotionally charged) comment from that moment lives on, potentially for years. The "energy" doesn't dissipate with time like it does in "real life".