I'm tempted to write that of course the gun nut libertarians will defeat the gun control fascist freaks, but that of course is not obvious. The United States is about as libertarian as an actual government gets, and it keeps looking for ways to be less libertarian. Gun control, morals regulation, hate speech protection, Patriot Act, nationalized health care...these are all anti-libertarian ideas advocated by members of at least one of the two major parties.
Part of the problem here is that it is not clear what libertarians and fascists are. Some of the answers have an exceptionally weird concept of what they (libertarians especially) are.
What's a libertarian?
I would define a libertarian as someone who is against economic and moral regulation. A Democrat is against moral regulation but is for economic regulation (both as regulations and through taxes to enable spending). A Republican is against economic regulation (especially taxes) but is for regulation of morals (e.g. pornography should be illegal).
Others find libertarianism to include an expansive reading of the fourth amendment. Opposition to the Patriot Act is rooted in this form of libertarianism.
You will also see opponents of libertarianism characterize it as "The only right that exists is that of property". I don't know that any libertarian actually holds that view. Most libertarians care about other rights (negative rights), like freedoms of expression, belief, association, defense, and privacy. They even have ways of unifying these beliefs, the non-aggression principle.
What libertarians do not believe in is positive rights. There is no positive right to have property. There is a negative right that your property not be taken from you. There are no positive rights to food, water, or housing. People have a negative right to freedom of expression that the government cannot take away but no positive right to an audience.
A reasonable definition of a libertarian is someone who believes in live and let live. They value freedom of action.
What's a fascist?
If we're going to be nice to libertarians, we should also strive to be nice to fascists. And if we put aside the history of fascism and look at people who are tarred with the label (those who do not consider themselves fascists but are called that by others), we can see positive things in their ideas.
Libertarians look at negative expression and talk about accepting the bad with the good. For example, the ACLU is about as anti-Nazi as an organization can be, but it still protected Nazi rights to speak and march. A fascist looks at the same thing and says that people should have a positive right to be protected from dissidence.
To the fascist, the positive right not to be offended outweighs the negative right to free expression. The positive right to be protected from violence outweighs the negative right to privacy from search and seizure, as well as the rights to self-defense. The positive right to transportation outweighs the rights to property.
The closest example to a positive fascist state today is Japan. They outlaw guns (and bullets) entirely. They won't even give waivers to allow movies with guns to shoot in Japan. To support enforcement, they have minimal protections against search and seizure. Any successful search was obviously justified. This is quite successful at preventing gun violence.
This is not to excuse the bad behavior of fascists. Many use the government power much less laudably, to suppress minority views or peoples. It's just to point out that positive goals can be achieved with authoritarian controls.
The fascist believes that it is the government's responsibility to ensure the important positive rights: freedom from attack; the resources for life; a proper education; freedom from being offended. They value safety.
Why fascism over libertarianism?
By its nature, a libertarian society leaves its citizens vulnerable. Criminals can speak and organize freely. Until they do something overt, they can't be prosecuted. Legal enforcement is reactive, after the fact. By contrast, a fascist government can be proactive. If a certain pattern of thought or action leads to criminal behavior in some cases, they can outlaw the pattern.
Most real governments operate in some place in between these two extremes. And most political parties pick and choose where to care about freedom and where to care about safety. In a truly libertarian government, that chooses freedom over safety everywhere, they will have plenty of opposition.
- Some will be offended by the lack of morals. They will want more regulation of "proper" behavior.
- Some will be offended by hate speech. People should have "proper" beliefs.
- Some will be concerned about insufficient resources for education and welfare for the poor. They will want more taxes for more spending.
- Some will favor increased support for law enforcement. More spending on police, who will be allowed to be more proactive in their policing. No more criminals getting away due to lack of warrants or paperwork errors. Guns and other weapons can be prohibited and confiscated. Surveillance.
Of course, if they succeed, then those things will create their own problems. In particular, the definition of "proper" beliefs differs from person to person. Out of power, multiple beliefs can ally with the same people. They each expect to prevail after victory. In power, only one actually wins. The others can join the libertarian opposition.
I'm not sure that violent revolution is the way to go. A libertarian government can always react to a violent revolution by becoming less libertarian. It can compromise its beliefs and respond. It is less able to respond to an electoral challenge. Initially, its opponents are the ones proposing compromise. They sound like the reasonable, accommodating ones.
They can take over the apparatus of government democratically and use that legitimacy to prevent a response. They can gradually replace the defenders of the old system with their own people. A slow increase in repression means that no individual act of repression seems inexcusable to most people.
A violent rebellion means that both the populace and the government are against the rebellion. Without the legitimacy of a democratic election, the rebels are immediately vulnerable to a counter rebellion. It also makes the opposition immediate. An electoral challenge allows them to concentrate on the popular aspects of their ideology.
Either needs popular support. A movement with enough support for a violent rebellion would seem to have enough support for an electoral takeover. And a libertarian government is ill-prepared to resist electoral takeover. After all, if that's what people choose to do, freedom of action says that they should be able to do so. Meanwhile, a violent rebellion can be put down with self-defense, by the well-armed populace with help from what government there is.
Becoming what you resist
Another alternative is to have a fascist rebellion that loses but leaves the country more fascist in response. Because we can't tell who is and is not a rebel, we confiscate all guns. Because the rebels were so bad, we outlaw the speeches that they gave. Because the rebels were most effective when they assembled into large groups, we outlaw large groups without licenses.
Once those kinds of controls exist, they are more likely to be used. Rebel speeches were bad, but so are those advocating lies. Or denigrating women. Or criticizing law enforcement. Or advocating against laws against speeches...