It comes from classical Liberalism and the social contract theory. Basically, by being born into a society, you make certain contracts with that society to accept certain responsibilities, such as to work, which you are free to do at any workplace of your choosing.

It's all voluntary, see, because you made that original contract by being born into a society that gave you life and sustenance. You definitely chose all of it, because I am definitely not trapped oh no not me the thought is simply too terrifying to even consider

(note, this is John Locke's take, which is hugely influential, and who actually had some pretty based ideas, ngl, for an ancient Liberal)