This doesn't say “prison labor is slavery”; it says that prison labor is allowed to be slavery. You should've provided some reference to e.g. a news article to back up your claim.
It's legal to paint yourself blue and write obscenities on your face and walk into a library, but that isn't evidence that anyone does it. (Likewise, it's legal to make people pay you fifty times the inflation-adjusted value of a loan you gave them – things being legal isn't evidence that they don't happen, which would be absurd.)
This doesn't say “prison labor is slavery”; it says that prison labor is allowed to be slavery. You should've provided some reference to e.g. a news article to back up your claim.
It's legal to paint yourself blue and write obscenities on your face and walk into a library, but that isn't evidence that anyone does it. (Likewise, it's legal to make people pay you fifty times the inflation-adjusted value of a loan you gave them – things being legal isn't evidence that they don't happen, which would be absurd.)