Although, we need to lock this. There's not exactly anything to debate or come to conclusions about, seeing as the OP's quote is from a troll who wanted this to exactly happen.
Good point. In the context of the OP, this sort of RP is obviously wrong.
But when I look at RP that crosses ethical boundaries from a broader spectrum, the response becomes less obvious to me. Not just because "RP is RP," but also because the act of RPing a character who crosses these boundaries doesn't necessarily mean an endorsement of his/her actions. The first example of this that came to my mind was Judge Holden from Cormac McCarthy's
Blood Meridian, if any of you have read it. The judge is certainly the smartest, best-educated, and most omni-talented of Glanton's merry little band of troglodyte Indian killers, and he never fails to amaze/manipulate/save the gang. He spouts philosophy, scripture, and all sorts of sciences. If it weren't for his antisocial mindset, pedophilia, and complete lack of moral center, he might actually be redeemable. But he isn't, and from the way he's presented, he can't possibly be construed any other way. His worse acts--pedophilia included--also happen without explicit description.
I see no problem with RPing a Judge Holden, ALTHOUGH RPing out more despicable acts, even in private, isn't something I endorse.