Why don't American cops enforce the law when they should?

I have written about this very subject before, but I think it deserves repeating because I see it on YouTube pretty much every single day, and to this day I have absolutely no idea why they behave like they do.

If you are in the United States, try going all on your own, alone, for example to a car of local law enforcement of federal agents, and damage the car in their full view, like slashing a tire or breaking a windshield wiper. What happens? You'll be arrested in a millisecond. You'll be lucky if they don't shoot you.

However, gather 50 people to accompany you, to show slogans and be all angry at the cops, and then go and damage their car. What happens?

In most cases, nothing. Perhaps one of the cops might shove you aside, but that's it. No arrest, nothing.

This is not hyperbole or just hypothetical. It happens all the time. Nowadays it happens many times a day. In the vast, vast majority of cases the result is the same: No arrests. The cops refuse to enforce the law.

Why? Just why? I genuinely do not understand.

And this is nothing new. American law enforcement has been doing this very thing for at least 10 years now, non-stop. Perhaps the only difference is that at this moment the mob is directly attacking federal agents and their vehicles, which should be even more of a reason to arrest them.

But no. 

News flash to American cops and federal agents: There is no exemption in American law that says that a crime is not a crime if someone commits it as part of a mob, as part of a "protest". There is no statute that says, for example, something along the lines of "destruction of governmental property is illegal... except if done as part of a mob of people." There is no such exemption in the law.

So why? For the sake of everything that's holy, someone explain to me why.

Do you know why they keep doing this to you? Because you refuse to uphold the law! That's why. You refuse to arrest and prosecute them for breaking the law. That's why.

Start upholding the fucking law already! It's not that complicated.