For a libertarian, they're not worried about that because they think they'll have enough guns to protect their.. uh, their bitcoin miner i guess? i'm not sure how they think they'll earn money.
I can't remember where I first heard it, but one of the factors affecting American politics in particular is the idea that many poor people see themselves as rich people in waiting. They're going to make it, once they get their break. This of course, is false for the overwhelming majority of poor people, but still causes their vote to skew further towards measures which harm them and favour the rich than it otherwise would, because they see themselves benefitting once they do finally make it.
And what is going to stop your "private police force" from simply taking control and kicking your out (or executing you)? A contract?
Edit: I would expect leadership in those circumstances to simply fall to the most effective leader in that kind of context (which I suspect would be someone from a military background) rather than someone who used to have a big bank balance. Give that a few generations and you'll end up with hereditary clan leadership and eventually "royalty" - all royal lines can usually be traced so some "stupendous badass".