I've worked in criminal justice for quite a few years, and the OP sets off a number of different chains of thoughts. Even though the idea of a website that helps you get romantically involved with a prisoner may sound like a good laugh on Valentine's Day, do you mind if I get serious for a while?
First off, there's the fact that for whatever reason, there's a large number of women (usually fairly young) who are fascinated by the idea of being in contact with a man behind bars. Especially if a prisoner is doing time for violent offences that have received a lot of media attention, there's a good likelihood that he'll receive a stream of love letters from total strangers. Go figure.
Second, there are over two million people in prison or jails in the U.S. (Random factoid: an estimated 12 percent of African-American men ages 20 to 34 are in jail or prison.) It shouldn't come as a surprise that young men who are locked up spend a lot of time thinking about women. The website provides them with a lifeline to the outside world, and who knows, the promise of better things to come.
This brings up a third chain of thought. Not all people in prison fit our stereotypical preconceptions of prisoners as being unhinged murderers and rapists. That population of two million includes a huge number of regular joes who - if you'll pardon the expression - aren't all that different from you or me. Leaving aside the question of whether imprisonment is an appropriate punishment for whatever it is that they did, the fact is that being in prison tends to increase the likelihood that they will reoffend once they are released.
Rehabilitating prisoners (however you understand the process) isn't easy. The first step is for the prisoner himself to want to change. There are a few things that might start him down the road - he "gets religion", decides to quite drugs or joins the AA - or he meets up with a good woman. The website might help.
Yes, there's a risk in deciding to get romantically involved with a person behind bars. But when you start to think about it, at least he's being honest about being in prison. The same thing can't be said for a number of the people you may get into contact with on the internet or meet at your local bar ...