My point wasn't about efficacy - frankly I don't believe it would be very effective, mass murder rarely is. Such a process would also require enormous resources, which creates a breeding ground for corruption. In practical terms - it would not be an effective way to achieve the goal and would open the door to many genuine atrocities.
My point was to put into perspective the point where libertarians ought to stop being libertarians - because of what becomes justified (justified != a good idea) when they do. People have a right to freedom of religion - but when you start believing you have the right to blow me up in the name of your deity I get the right to shoot you first. People have a right to freedom of speech - but when you are advocating that people should kills gays - we bloody well will lock you up, even in the USA. On the other side - I am (a kind of) socialist in my thinking, but at the point where socialists advocate violent revolutions I no longer support them. Those have historically caused massive hardship and slaughter of innocents, installed dictators and consistently failed to produce socialist outcomes anyway - the most successful socialist states achieved it by peaceful and democratic processes.
No matter how good your idea is, no matter how nobel your goals may seem to be - all ideas have limits, and that limit is where other people can make a reasonable argument that your pursuit of this idea puts their welbeing at risk.
Even if libertarians claim they would offer workable alternatives to government prevention (and so far none has - all I've heard is 'recourse' which is the old Murray Rothbard argument and doesn't offer anything resembling a workable solution but they like to push that one because it *sounds* like the are solving the problem without actually stopping anybody from killing you) a sane version would declare that all laws and regulations on matters of public safety will stay intact until AFTER their alternative systems are in place, tested and working.
You don't create a vaccuum in which slaughter can happen while going through the arduous process of building something else, even if you think that something is better (by whatever measure you decide it is better). You build the alternative BEFORE you dismantle the current one.
Because a bad system for public safety is still better than none at all, even if it's briefly - and legal changes are never 'briefly'.
I absolutely do agree that the best way to deal with the particular threat posed by libertarians is not through killing them in self defence. Hell even if somebody attacks you and wants to kill you right now my belief is that you shouldn't kill him in self defence if you have any other options. If you can escape - then you shouldn't kill. If you can disable without death then you should take that option.
Killing, even in self defence, is a last resort. I wasn't advocating we kill libertarians - I was merely putting into perspective the risk they pose. If you believe in libertarianism, fine, we will never agree but we can live alongside each other. On issues of social liberalism we could even be allies even if our economics will always be as opponents.
There's nothing wrong with that. But you ought to stop being a libertarians BEFORE the point where it risks the health and safety of other people. Just as you ought to stop being a christian BEFORE the point where you bash gays.