Yes, having more liberals working in policing is probably more inline with the goals of those liberals than not, but that's not the point of a boycott.
If the police can't get the help they need from mathematicians because of a large enough boycott then it gets them to the table and forces them to reform.
I'm not arguing whether or not this will work, or making a value judgement, I just see a lot of comments which don't seem to understand this point.
If not, this will make someone unhappy. And this is the whole point of boycott.
The police is making mathematicians unhappy. Bad cop, no donut in any dimension.