I agree with Bruce.
The more veritcal, the more dangerous throw.
But abruptly stopped throws/movements are also very dangerous.
But I don't understand Christians problem. I do understand there was a problem, and it included a wall. But I don't understand that a udekemi-nage should give a problem like that.
As I see it uke has responsability to himself to take care of his ukemi. He shouldn't just "let go". The moment a throw is started, uke has the possiblity to ajust his ukemi, so he doesn't hit a wall or fellow Aikidoka.
But mybe I could see it one day.