Oh boy, This will be a nice ungrateful task of playing the devils advocate.
First I'm not taking his/her side in this case if he/she actually is a predator he/she can slowly rot in
hell.
Now you made a disturbing discovery but I wonder did you get any complaints about him/her?
What concerns me is that you alone took action in banning a account based on some non quantifiable facts (age, gender)
that might hint he/she is a predator.
But there is no real proof - at least you don't disclose that information in topic start.
A male member - Is he a male?
Who interacted exclusively with girls - Are they all really girls?
Nearly all of them under 18 - Are they all under 18?
Being quite aggressively flirtatious - Like most young adults.
And expressing interest in meeting them, with no reservations about their age or how far from him they live. - Okay you
got me there but it wouldn't stick in court. ;)
Spamming, Trolling, Ripping etc all can be used to warrant a ban .. But a gut feeling?
Of course I realize MT isn't a democracy and Staff can do whatever they wish to do.. :)
but because people are so curious and I don't feel any personal obligation to
protect his privacy,
This is plain wrong .. and in some countries you actually could get sued over this. (slander)