So one of the weird things about the anarchist movement is how few of them actually advocate revolution. Most anarchists believe physical resistance to the tyrants is impossible and that we can win using a combination of nonviolent methods:
The most notable one is agorism, which involves "counter-economics" - economic practices that undermine the state's control. Agorist Filthy Heretic has a 14-minute interview with IdeoLogs that explains agorism well. Agorists are usually big on things like cryptocurrency, privacy and decentralization.
Culture warfare. Many of them think the primary way to end the state is to convince enough people to recognize its illegitimacy.
Civil disobedience. The theory being that if a sufficient number of people peacefully refuse to obey unjust laws, police will be unwilling to use the amount of violence necessary to enforce them, and that will collapse the state.
Secession or seasteading. The free state project is an effort to basically concentrate libertarians in New Hampshire, and seasteading is the idea of building floating societies outside of the claimed territory of states (I personally find seasteading the least practical idea here for several reasons).
Unfortunately, no strategy that doesn't end in revolution will work. Agorism and seasteading seem to ignore that governments will use violence against any such movement that constitutes any real threat to them, like they did against Ross Ulbricht. Culture warfare and secession assume that statists can be converted, but the vast majority of them are entirely closed to reason; most statists suffer too much from status quo bias (and many other factors) to be convertible until they see an anarchist movement succeed. An anarchist movement that depends on converting more than a tiny minority of the population will never be successful.
Thinking civil disobedience will be successful is just silly because of both what we know about the nature of governments and the track record of police attacking peaceful people. Police don't feel responsible for their actions, and even if they did, most of them are monsters who don't care.
None of this is to say the above strategies aren't valuable. Culture warfare and counter-economic activity are obviously important parts of a complete strategy. But they won't be sufficient. Defeating a violent criminal organization requires defensive force.
You don't have to be an anarchist to recognize that at least most laws are unjust, and the police regularly arrest or even murder people for things they know are victimless. You also can't raise the "if I didn't take the job, someone else will" defense for them because police don't work that way. They don't have a membership quota that they draft for. People who join do increase the number of them and the power of tyrants to enforce their edicts. Politicians are also generally guilty in the same way as someone who orders a thug to attack you - just because they aren't personally the one doing it doesn't exempt them from defensive force. We must avoid the mistakes of the immediate threat doctrine; violence against someone who has committed aggression before and will continue to do so is certainly defensive violence, even if they aren't immediately engaged in it.
Police are stormtroopers. If you think it's ethical to shoot a stormtrooper without being shot at first, but not to do the same to a cop, ask yourself what the difference is.
It wouldn't even be murder to kill a cop you knew had never arrested anyone, because signing up to be an enforcer for unjust laws is a credible threat of violence against anyone they might hurt in doing so. To remove biases, imagine witnessing me sign up for a mercenary organization. The recruiter tells me "you will kidnap people who do things I don't like, kill them if that's what it takes, and I'll pay you" and you hear me agree. Is it murder for you to kill me, given you have no other way to stop me from going on to commit those crimes?
Proportionality of force defenses are weak. Someone doesn't have to be guilty of murder exactly for lethal force to be justified; for example, it would be moral to kill a rapist or kidnapper if it were the only way to stop them. Also, police frequently do commit murder in the enforcement of unjust laws, and life imprisonment sentences can be even crueler and more harmful if less salient to us.
The only real argument against it being morally legitimate to kill police is that not all of them do enforce the laws as they promise. Certainly, it would be wrong to harm one you knew intended not to enforce unjust laws. But that doesn't make a convincing case for them in general, because if you knew that there were some Nazis who refused to arrest Jews, it wouldn't suddenly void your justification for shooting at Nazis.
All that said, there is a good reason not to "start shooting": conscientous people currently lack the numbers to revolt successfully, and an unsuccessful revolution could be counterproductive; most people will perceive a revolution as a crisis (especially due to government control of news), and so if it's crushed by the government, they'll learn one more time that government violence is the solution to their problems. History is written by the victors.
But revolution is at some point a necessary part of our strategy. Not now. But it is a necessary part of it. No combination of strategies that excludes defensive violence against the enforcers of tyrants can have any reasonable hope of success.
One common objection that isn't to the ethical justification of revolution is that it has historically resulted in a new government. This is a terrible argument because the people behind most of those revolutions were not anarchists. They never had any intention of freeing their society. It would be ludicrous to assume things will play out the same when a revolution is carried out by people with such vastly different intentions from the get-go.
In general, people vastly underestimate the feasibility of revolution; especially because an anarchist revolution would have an easier goal than historical revolutions like the one that led to the foundation of America. It doesn't aim to establish a new authority. It only aims to make oppression impossible. In reality, an anarchist revolution could succeed with an incredibly tiny minority of the population and without killing even most politicians or police. Reducing the number of police to a number insufficient to enforce laws would be a sufficient win condition. If there were only enough cop-killers to make being a cop too dangerous a proposition for anyone to want to do it, we would win. Theoretically, we wouldn't even have to kill most of them.
And mass-destructive military means like tanks and bombing wouldn't even be effective against such a revolution, because there would be no targets. Anarchists wouldn't have a capital or military bases. The people posing a fatal threat to the government wouldn't be an army marching on a government bulding, but the ordinary person who shoots you when you try to arrest an innocent.
I don't believe revolution would be successful now, but only because the revolters would be far less than even 1% of the population; even most anarchists don't seem like they'd be involved. And that's if we assume no one declines to participate out of fear rather than out of ideological opposition.
One thing I've always been frustrated with conservative minarchists about is how openly they talk about how the purpose of the second amendment was to enable the people to revolt, how they realize the US government is far worse than King George ever was, how they're fully aware that 99% of what it does is unconstitutional, but still think it would be murder to kill cops or politicians. My diagnosis is that their talk is a sort of venting they use to quiet the good in them so they don't end up admitting to themselves that there's no difference between a cop and a stormtrooper. It's shocking that even most anarchists are the same way... although anarchists usually admit there's no difference, but in practice still judge as if there is.
Larken Rose has some has some excellent further reading on this.