The problem lies not in that you are wrong in concluding that these people are adherents of leftists ideologies (most are), but that you are falling for the pars pro toto fallacy: people who think that 'master' is an offensive word to use in a source code repository are 'left/liberal', thus all or most of 'the left/liberals' are such people.
You are saying 'this group thinks' as if all people who would identify as adhering to leftist ideologies (from the extremes to common social democracy) act like this. You are trying to stuff people into boxes: you are either team A or team B. That is polarization; something we can sorely do without.
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.
I think you're right. I'm an independent and I'm guilty of doing this to right and left leaning folk, but I've done it because I believe that the people screaming will only listen to people within their ideological interests. It was my way of making them accountable for their compatriots that are loud enough for me to notice. I've also stopped doing this because it's not really effective. People don't feel like they should be responsible for outliers and I somewhat agree, but don't know how to solve the problem of vocal trouble makers.
The problem lies that there is not enough (any?) push back from this kind of garbage (and specifically in this case) from the 'left/liberals'.
There needs to be push-back if they [those left/liberals not in this camp] want to disassociate. But where is it? I don't think there is appetite for this argument.
I know many of left/liberal-types (in the Bay Area) all who either believe, or accept this as silly but somehow think it is meaningful to some people and so should be gone along with...
You are saying 'this group thinks' as if all people who would identify as adhering to leftist ideologies (from the extremes to common social democracy) act like this. You are trying to stuff people into boxes: you are either team A or team B. That is polarization; something we can sorely do without.