Some people oppose governments on the principle that they are organised gangs of thugs. They consider the defining characteristic of governments to be that governments claim the right to initiate force ... and people listen (whereas most thieves don't pretend to be legitimate and aren't considered as such). They point out that they never agreed to pay taxes, and don't want to, and don't like most of the stuff the taxes pay for, and consider that QED.
Some of these people support the war on terrorism. They realise that terrorism is a large threat, and want it to be fought against. Terrorism is so bad that anyone at all fighting it is good. I suppose they must see the matter as a powerful pickpocket guild beating up a renegade gang of murderers. A "lesser of two evils" situation.
Some of these people, if given the option, would be happy to see the US government disappear tomorrow. The institution, the knowledge of how to run it, the taxes, the laws, etc This is absurd even within the pickpocket metaphor, as it means foregoing protection.
But there's more than that. The government does various things, some important. And it's not as if the spontaneous order of an anarcho-capitalist society will simply come into being. AnCap is not the natural state of affairs that once existed until it was destroyed when a bunch of evil thugs invented government and took over. It is, rather, a very advanced notion that requires lots of knowledge to implement. This knowledge must be created gradually, through the improvement of existing institutions. Government functions must not disappear over night, but slowly be replaced by private institutions that function better. We need good traditions, not a revolution.
What's good about government?
Governments create consent. Let us imagine a bunch of people living somewhere with no government, and little knowledge. Some will be bad, and will want to dominate over the others. So most people will form mutual defense pacts. And somewhere not too far off, some bad person will have taken over an empire, and formed an army, and thus our people will want to form one big defensive pact, instead of lots of scattered ones, so that they can fend off the entire army if need be. So they will form institutions to cooperate in regional defense, and small-scale defense against criminals. The small-scale defense may use a different system, or the two may be joined. Now, the people will need some system of deciding who is and is not a criminal. And the answer to this is not self-evident despite what some libertarians seem to think. There will be disagreements, and thus some way to resolve them will be needed.
One day, Joe's crop goes bad. He asks others for help. They form some food sharing institutions. They create rules to govern these. The people all value security, and thus put in provisions to help anyone who does not have enough.
One day they invent medicine. They realise that if they only pay the doctor when they are sick, he will starve in the mean time. And also that he will have no motivation to help prevent people from becoming sick. So everyone pays a low level all the time, and the doctor helps whoever needs help at recovery and prevention both. Some people disagree about who the doctor should be helping, saying he favours his friends, and they create institutions to resolve disputes of that nature.
What will all these institutions look like? Well, at first they will be very crude. The defensive agreement might simply state that all able-bodied men must fight when there is a war, or be put to death. The food agreement might allow anyone who is starving to take food from his neighbor, "as long as he made a genuine effort to create his own food." And the system of resolving disputes might be to ask the town elder.
And, over time, people will come up with better ideas. And after a while, and a lot of progress, something like our current government might form.
And, if this society uses a completely voluntary army, that will be an amazing advance. And if it has elected leaders who consent to step down when their term ends, that will be an amazing advance. And if criminals are presumed innocent until evidence is presented against them, that will be an amazing advance. And if there are property rights, and a system of consensual trade, that will be an amazing advance.
When we know how to do better than using government, we will. But we do not. And the path to better is not to rail against the government, but rather to acknowledge it for what it is -- an imperfect, evolving tradition. The path also involves raising the general level of morality of the world.