It's not that the police suck at infiltration, it's that the law makes it extraordinarily hard to prosecute these people for the most absurd reasons. People need to stop hating on the police and hate on the bureaucracy that has been scapegoating them for over 300 years because the police are even bigger slaves to bureaucracy than your average citizen, they effectively have no will of their own.
Imagine what it's like to devote your life to protect others because you genuinely care about others as if they were your own family, your family that you hardly ever get to see and constantly worry that you are putting in danger - a guilt that slowly eats you away inside, getting paid shit and unable to get rid of the bad guys because they have more power than you in the long run, and every time you follow some bullshit order that you know is wrong because lawyers are fucking psychopaths, the very people you try to protect hurl abuse at you. Why do you think so many of them look dead inside? I say all of this as somebody who kills people for fun. And I promise you that you people, all of your positive affirmations don't mean a thing. That's all I have to say, well that and if you're not willing to take responsibility then you have no right to complain.