Can you unpack and justify this statement?

People are generally content to sit back and do nothing if they can get away with it. Getting people to be active - in the work force, in the government, in the culture, whatever - requires the people to see a need. Otherwise, they'll sit at home and drink/screw/watch TV/play video games/whatever, because it's more fun. Creating a system where people are told not to worry about their fellow man, because someone else is, means that they mostly won't. If that system actually does take care of other people, it can trundle along well enough, but if it fails to do so in ways that the public doesn't pick up on, those holes won't be filled, because people will think "Oh, there can't be a hole there, the government would have fixed it if there was". If the system ever gets disrupted, people who have lost the habit of looking after themselves will be in real trouble.

I'm not saying "Throw everyone to the wolves and let the strong survive!", but I am saying that independence is a muscle that needs to be exercised once in a while.

Have you looked? I mean, for one thing, which government, of which country, under which system?

Yes, and all of them. The incentives just aren't right for any government, full stop.

This statement is either tautological (ethical proprietarianism) or simply wrong.

It's neither. It's a claim of economics, not ethics or logic. (There are non-taxation causes of deadweight loss, but they're fairly rare outside of taxation). http://en.wikipedia.org/wiki/Deadweight_loss