This is, I think, partially the result of decriminalization. When a vocal sub-population says "oh no, but poor people have no agency, and therefore no choice b

This is, I think, partially the result of decriminalization. When a vocal sub-population says "oh no, but poor people have no agency, and therefore no choice but to commit crime / evade fares, etc. and we should be more lenient" this is the result. And the people who suffer the disproportionately are the working class who rely on public transit. Even if BART doesn't have enough officers, spending a few thousand to put up high-def cameras so some other PD can kick open these assailants' doors and arrest them would help significantly.