Exactly nothing because you can release the seat belt yourself.

It's about giving up freedoms you might never get back, because it's not your decision anymore after giving them up.

It's become more a shorthand for saying much more. Though the original context differs from how it is used today (common with many idioms).

People do not generally believe a seat belt limits your liberty, but you're not exactly wrong either. But maybe in order to understand what they mean it's better to not play devil's advocate. So try an example like the NSA's mass surveillance. This was instituted under the pretext of keeping Americans safe. It was a temporary liberty people were willing to sacrifice for safety. But not only did find the pretext was wrong (no WMDs were found...) but we never were returned that liberty either, now were we?

That's the meaning. Or what people use it to mean. But if you try to tear down any saying it's not going to be hard to. Natural languages utility isn't in their precision, it's their flexibility. If you want precision, well I for one am not going to take all the time necessary to write this in a formal language like math and I'd doubt you'd have the patience for it either (who would?). So let's operate in good faith instead. It's far more convenient and far less taxing

The quote refers to a Faustian bargain offered by the Penn's. They'd bankroll securing a township, as long as the township gave up the ability to tax them. The quote points out that by giving up the liberty to tax, for short term protection, ultimately the township would end up having neither the freedom to tax to fund further defense, or long term security so might as well hold onto the ability to tax and just figure out the security issue.

Moral: don't give up freedoms for temporary gains. It never balances out in the end.

You dont deserve either.