So does usury.

You loan someone $40000 @ 5% APR and he spends it on education. If the loan is to be paid back in a decade, he has to cough up $416 per month. Unlike a mortgage, he can't foreclose on his education.

Since he doesn't have any assets to sell, and is by law unable to get out of them through bankruptcy, his only choice is to work some amount of hours every month to pay off the loans.

If that is not slavery, then surely ISAs are fine too? And if that is slavery, then how are ISAs any worse?

but it's not like slavery because you can quit at any time. Outside of blockchain contracts should be considered 'Slavery' because an 18 year old can take out a loan that ruins his whole life because he is forced to pay back the loans by some outside entity. Investing in an individual via the blockchain makes it so you are investing because you believe in the individual, but at any time the individual can simply stop working, stop earning and enjoy a simple life without any repercussions. This makes the investment more risky for sure, but stops it from being slavery because a.) the individuals don't have to be worried about some gun forcing them to do something b.) i can sell my tokens at any time.