Restraining an attacker w/out injuring her/him.
It seems to me that it would be very likely that an attacker would be injured in even some of the milder techniques if they were applied by someone with less experience. Even with only a few lessons, an aikidoka could probably manage to utilize at least one of the simpler techniques..or even just iremi or tenkan out of the way. But applying any of the take-downs without injuring the attacker would rely on a huge number of factors. Even a perfectly executed kotagaeshi could injure the attacker if it were performed in too small a space (head meets wall with predictable results) or on ground that was uneven..(I'm picturing an alley outside a bar with broken glass etc.) But even larger spaces, when unfamiliar can lead us to injure ourselves..I whacked my foot but good coming out of a backroll because the wall was not where I expected it to be while visiting another dojo yesterday. When practicing, uke may resist some of the techniques in so much as he or she will not allow you to take them down with an insufficiently applied form..but at least when they fall they are relaxed and falling onto a mat..not to mention that they have practice falling!
From the amount of pain that I went through learning to fall...even without significantly injuring myself, I would be inclined to believe that an attacker being injured in at least some *small* way is very likely unless the skills of the aikidoka, the physical and mental state of the attacker, and the environment all cooperate to prevent such injury. Which seems unlikely seeing as Murphy's law is almost always in operation.
"Are you *sure* this is safe?"