You can become someone's slave if you really want to. The only part that can't be enforced is you can't be coerced to stay.

Plenty of cults have slaves in the US. But because the are willing, nothing is done about it.

Heck, plenty of us companies still rely on slave labor. Look at Aramark's use of prisoners, for example.

That's an explicit carveout in the Constitution allowing slavery as punishment for a crime, not someone waiving their rights.

This reminds me of Futurama:

"You know the worst thing about being a slave? They make you work, but they don't pay you or let you go."

"That's the only thing about being a slave!"

So yeah, you can legally be a slave as long as you leave out the one part that makes it slavery.