I got the feeling that Starfleet or the Enterprise put a warning bouy in orbit to stop people ever coming to or entering that System.
General Order 47? :P
I actually quite like Skin of Evil, mainly because I think Armus is a really cool creature. Having him scream in pure rage as Picard basically flips him the bird and beams off is excellent.
However, watching it with a friend recently, he pointed out that it's not a very Star Trek way of dealing with him - and I have to agree. I don't like Data saying he should be destroyed, and I don't like him being marooned on that planet for all eternity.
Picard should've requested a ship be sent to collect him for study in the hopes he can be rehabilitated - or at the very worst, humanely euthanised.