I'm not sure if you're being sarcastic or not with your final sentence. But assuming you aren't. If they did their time, they did their time. Why not ban anyone with a criminal conviction?
>Assuming those people are actual, proven, and unanimously agreed upon sex offenders
How do you prove this to the computer? Have a representative manually handle every case with a sex offender to see if someone is too perverted to join their network? Surely that's a PR nightmare. "Well he had sex with a 17 year old girl, so we're fine with him joining. But a 10 year old boy, that's where we draw the line."
The list of sex offenders is more than just a list of child molesters. Public urination or indecency and anything in between goes on there. All of them are bad to a certain degree, some of them terrible. But if someone has served their time, we should not continue punishing them, but give them a chance to reform.