Like most conservatives, perhaps all, I'm a law and order guy. I have tremendous respect and admiration for the police, and count several among my friends over the years. Every police officer I've had to deal with has been as professional and courteous as the situation allowed, and they have a very hard job to do.
That said, cops aren't always right, as an honest police officer would be the first to admit. Sometimes they mess up, and when they mess up it's a bit more important than when the pimply teenager forgot the onion rings in your drive through order. Sometimes they mess up so bad they cause some serious damage.
For example, a cop bashes your door in and invades your home with a gun, demanding you surrender. Turns out he meant to get 1577 Oak street, not 1575, where you live, and now he owes you a new door and years of therapy for your traumatized kids. This doesn't happen very often, if for no other reason than they'd never live it down with the other cops. But it does happen sometimes.
There are other instances where cops unlawfully enter a home. In Indiana, a supreme court case examined this situation, courtesy Orin Kerr at Volokh Conspiracy:
In this case, the officer had come to the home in response to a domestic violence call. He found the defendant, Barnes, outside. The officer and the defendant exchanged heated words, and the defendant started yelling at the officer. The officer threatened to arrest the defendant if he didn’t calm down, and the defendant threatened to have the officer arrested if he arrested him. At this point the defendant’s wife came outside, threw a duffel bag in the defendant’s direction, and told him to take the rest of his stuff. She then went back inside the home. The defendant then reentered the home following his wife, but once inside he blocked the officer (and another officer) from entering. The officers asked if they could enter the home, and the defendant’s wife pleaded with the defendant to let them enter. The defendant refused. The police then entered anyway, and the defendant “shoved [an officer] against the wall.” The officers then tazed the defendant and arrested him.
The defendant was charged with misdemeanor battery against a police officer, among other things. At trial, he wanted to argue to the jury that it was lawful to shove the officer because he had a citizen’s right to reasonably resist unlawful entry into his home.
This case went all the way to the supreme court, who decided that you can't fight a cop even when he breaks the law and invades your home. The court argued that, while in the past, common law provided for people to fight back against legal authorities for invading their home improperly, these days there are legal means to deal with it, so its illegal to fight the cop.
This ruling is part of a basic judicial principle these days that violence is necessarily bad and wrong, and, further, those old Founding Fathers and previous legal scholars were old fashioned, and that doesn't apply these days.
This ruling is very wrong in my opinion, and further establishes a very uncomfortable precedent in American law. Already it is illegal to lie to federal law enforcement officers, when freedom of speech should permit people to lie to government officials, if anyone. By creating a separate, superior class of people in law enforcement, the U.S. moves closer to the very things the U.S. was founded to fight against.
Anyone invading your home - police or otherwise - in an unlawful manner triggers your right to self defense. If there is one principle held higher than almost any other by the Founding Fathers and American history, it is that every man may defend his family and property. That's the idea behind "castle laws" like the one on the books in Texas: you can kill to defend yourself and your home.
Police are not somehow immune to this feature of American law and philosophy. If you invade my home illegally, you're breaking the law and I have the right to use force to defend myself and my home, period.
The idea that people can use the legal system to address grievances is accurate, but insufficient. People have always had the legal system to do this with - even in England, the land the Founding Fathers fled seeking liberty. It wasn't always perfect and it didn't always protect people, but neither does our system now.
Violence is a tool, like the legal system, rhetoric, and many others you can use, to fight injustice. The courts want to remove that tool from citizens, and that's something we must always and vigorously oppose.