Have you ever met a cop before? The only disincentive to arresting more people is a bit of paperwork, and the whole court system is stacked against the arrested unless they can afford non-court-appointed lawyers to pave their way. Guilt-by-association doesn't magically disappear from the psyche when handing someone power and a gun, rather it gets easier to apply indiscriminately because it's very hard for people to oppose the one with authority over their freedom and state-sanctioned license to be violent.