I don't think it's fair to say that most cops are cowards. Just a few cops who are bullies or corrupt can cause a lot of damage and they tarnish the reputation of the good ones.

Interesting story: I'm an admin for a Facebook group that has thousands of members. The other day another admin had to get rid of a member who was causing trouble and making threats. After threatening the other admin he banned him. Then the guy made a threat on his personal account, so he had to block him there. He said he was a cop.