I think that more accurately it can be said that "An Aikido practitioner can control the attacker without injury". If a practitioner is at a level where such a choice actually can be made, then that is all there is to it, just a choice.
OK, if "An Aikido practitioner
can control the attacker without injury" then there is no need for ukemi. And if that's the goal (I'm not saying that it is, or should be, just IF), then why are you training people to throw in such a way that ukemi is necessary - since that is contrary to the stated goal.