Is rape and constant sexual abuse inevitable for young men imprisoned in the US?

Cops in shows like L&O are always warning suspects that they’ll end up as someone’s bitch if they go to prison. Are things really that bad? Do the prison authorities take active steps to protect young men from sexual abuse, or do they turn a blind eye?

I know from some of the comments US Dopers have made in the past that some people almost consider prison rape as part of the punishment, especially for particularly odious crimes.

Amended title from teenage to young men. I really mean vulnerable, young, inexperienced guys.

Previous threads on prison rape, generally: