Pokemon are active creatures, I don't think they can stay still for too long. I suppose it depends on their level of patience.

That implies the ability to steal souls differs from the normal ability of a pokemon; there is the possibility it is a normal attack. If abilities can be forgotten by some means, it might be possible to remove the ability that way. There might be technology for that, it is advanced enough here, but people don't seem to be utilizing it as much as they could be. Professor Oak might hold the monopoly.