But it's a bit more complicated than that. Many people refuse to believe that their friends have done something "wrong" and will water it down in their own minds. Much like when parents refuse to believe than little darling Johnny could ever have done something like that.
I agree, the police force as an organisation (in each country) needs to put more focus on their members behaving property, and expelling those who don't, but at the same time, it's hard for people to punish their own friends (which are usually the people who are with them on the beat, and know they've done something wrong). Or they'll even believe that the act wasn't wrong.
Also, many police who would otherwise dob in their comrades do not for fear of repercussion.
There needs to be organisational change, but to call 97% of them bad is either mean-spirited or naive.