Just because someone said that they aren't horrible people doesn't mean that they're presenting them as model citizens. There doesn't have to be anything "good" about them, it's just a decision, which can lead to all kinds of things.
If issues lead to behaviors, some of which being bad, then why not isolate the issue that leads to bad behavior instead of dismissing people based on a behavior that may, possibly, be linked to behaviors that are actually harmful.
Having sex with people doesn't hurt anyone, and promiscuity is not the direct result of "issues", though it can be... just like everything else.
The world is a lot brighter when things aren't seen in black and white