The problem with your perception of events is double:
1.For one, the Constitution (and modern American law) is equipped with various tools that do allow for rapid change. Judicial impeachment, independence of the three branches of government, the unified executive, and the pardon power are all useful here.
But more importantly, you are operating on the premise that there is some 'power' to a revolution that is issued to someone, somewhere, by some document. The truth is that a revolution – peaceful or otherwise – is a power that cannot be takn away. Once enough people want a revolution, it happens. Now, the number of people needed is lower in the US than it is in, say, North Korea, for obvious reasons such as the availability of free speech.
The Founding Fathers understood that the US government may one day become tyrannical, and they explicitly installed moral approval of changing the system of government when that happens. It's there in their writings, and in the DoI in particular.
Once a critical mass of people is dedicated to a revolution and equipped with competent leadership, the revolution tends to happen. It's difficult for me to understand how it is possible for people NOT to have that power.
2.Suppose you were unjustly imprisoned. Surely you would want to be freed today. You would not want whatever political movement which favored freeing you to dawdle for forty, fifty years as they enacted moderate reform, right?
In the Eugeny Shwartz rendition of “Don Quixote”, Don Quixote is woken up at night hearing the “Voices of the Unjustly Punished”. They repeat merely: “We are the Unjustly Imprisoned. Do you hear, good knight? You are free, we're in chains! You're free, we're in chains!”
There are literally thousands of people imprisoned under various laws which libertarians (and some conservatives) consider unjust. This thread is not the proper place to debate these laws, but here's my point: from a libertarian point of view, objective morality exists. The suffering of these people is an act of injustice going on every single day.
From a libertarian point of view, no-knock warrants, drug enforcement, and so on, is an act of constant injustice, the same as slavery was. The various laws enabling the state to apply fines, arrests, and imprisonment to activities from 'not wearing a helmet' to 'having a gun barrel an inch too short', or prohibiting people from selling and buying certain items, are an injustice. (And let's not forget there the thousands of options we'd have if society was freer that we're not even aware of.).
Every single day that goes on, a person goes to prison for some violation of these statutes, or dies because the development of a cure was held up by some FDA regulation, or maybe gets his home or car confiscated under forfeiture laws. Or maybe they just ruin his life with a conviction and let him go.
And I'm not even talking about stuff that happens in countries less fortunate than America (though I think the problem is with the entire Western world).
If I lived in America today, I'd be pretty much free to do the things I personally want to do with my life, (apart from owning machineguns*). I'm not a big fan of the forbidden pleasures. But there are people out there who are really suffering, who really need help.
The libertarian concept is tied intrinsically to the idea that objective morality exists. If an immoral status-quo, an oppressive status-quo exists – like it did with slavery, the solution is not to try to deal with it over a course of seventy years. Thousands of innocents people will live out their lives in prisons, or be shot in police raids, or have their lives otherwise destroyed or limited by the State by the time you're done.
If, within my lifetime, I will help free one drug-law inmate, or shorten the lifespan of the System by one day, then I have done something with my life. The difference between me and a conservative is that I feel the moral duty to work as hard as I can to end the System as fast as I humanly can.
*Yes, I know that if I were an American citizen I'd have the wondrous freedom of choosing from a selection of 200,000 guns manufactured 23 years ago. Even if I had the coveted citizenship (which, as you all know, is the primary goal of my life), I would prefer not to partake.
