Most startups fail - when a company fails people pick themselves up and go and do other things, generally a bit wiser for the experience.

History suggests that when countries fail, or at least when the machinery of civil society fails, things can get very unpleasant.

I suspect that this may be merely a problem of granularity. Countries have been located on a permanent continuum, not on many discrete little movable platforms. If a seasteading nation failed, the pieces would just get sold off and towed away to simplest that is civilized.

Just like Yugoslavia? It isn't that simple. Guns come out when sovereignty gets threatened in this way, especially if things have deteriorated to the point that lots of people want to leave.

Yes, but before, you couldn't tow your land away. Borders don't work quite the same way. Sure, you can bring out the AK-47s, but then you're going to get in the Zodiac with your cronies and motor over to...a reinforced concrete platform 60' above the water...and those guys have AK's too and you have to climb a ladder up to the platform? I don't think it's quite the same deal.