I'm gonna side with Kerry on this one.
I've tried playing guitar with a pick, and to be honest, it's just no fun. It's about as bad as when us guys have to use a --- err --- I better not complete that thought. :-)
Let's just say, you really can't get a good feel for playing the guitar any other way except when you have those long fingernails.
Not being a guitar player, I'll grant you that. :o)
But the only thing I can imagine is fingernails bending backwards on steel strings. Ouch!