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.
They will just hire someone else. Google was making AIs for the chinese government that almost certainly have deep ethical issues and it was barely a thing. Now helping the police is a boycott issue?
The question is not "do the police want a seat at the table", its if you want the people working with police to be only people who disagree with you and reject your position?