I've never heard of the assertion that an Aikido practitioner can control an attacker without injury. Yes not withstanding Osensei did his best not to injure guests in his demo, his own students suffered injuries when they failed to take proper ukemi from him.
Good aikido does not force injury on uke. It just returns the amount of force the attacker used in his attack. And if uke cannot do ukemi well, that force may graduate to something that is dangerous as we increase our intensity. Nage's only being nice when he slows down your attack.
Case in point is Ikkyo. There any number of ways to take ukemi from one. But if uke thinks that the choice of ukemi is his, then he'll be in for surprise when someone who really knows his Ikkyo lets go one time. Or better yet iriminage. Everyone things hmm, back fall or flip yeah? Until the guy lets rip and you find him doing a hula hoop with your neck, and your legs are making circles... Or bounces you of the ground and you find yourself flying forwards with your legs in front of you.
In all cases when I find myself unable to choose an ukemi, I just pray that my body would do something right when I hit the mat. It's always a happy feeling to find myself still alive after one of those. But in all those events, never have I felt nage was out to hurt me or throw me. It always felt like I got caught in a whirlwind and was loosed after a time... Does that make sense? The hurricane's not out to get you... You just happen to be on its path.
I don't know where you've been, it's even on Wikipedia
, and it even used to be on the Aikikai Hombu home page, before they rewrote their description. Also see the old Koichi Tohei description in "Aikido and the Dynamic Sphere".
Anyway, if the choice it "take ukemi or be injured" then I think that the average person will end up being injured (since they have no idea how to take ukemi). I don't necessarily have a problem with that - but it vastly changes the dynamic. The standard way of training while taking ukemi trains the nage's body to expect a situation that - just doesn't occur.