Again, availability bias. The people screaming the loudest about this are also screaming the loudest about other Left/Liberal issues. The normal left-leaning folks don't get heard. It's pretty natural to conclude that this group represents the whole.

I'm also convinced that the screamers aren't really interested in stopping black people from being offended (let alone actually harassed/murdered). I think they're much more interested in getting recognition for fighting the fight.