If aikido techniques are so "safe", why is so much time spent is teaching ukemi? Why the concern with breakfalls?
I've thrown people several times on concrete and they were not seriously hurt — just stunned and surprised.
Muggers or people who want to fight are usually young, fairly healthy, and pumped up on adrenalin and maybe drugs and alchohol. Because they are caught by surprise, they usually fall well and naturally because they have no time to tense up from fear.
In the dojo, conditions are different. People see others taking breakfalls, they have time to think about it, tense up and become afraid.