i don't question the conditioning of the body using the right approaches. i question the whole point of breaking your body to prove that you are tough to take on things. Ellis Amdur wrote about someone went to Iwama to practice and got his arm busted that he could no longer use it, ever again. how would losing the usage of the arm helping self-defense? that's my question. take Kevin for example, while healing from his injury got jumped, what would his chance be compare to when he wasn't injured. hard practice and smart practice are two different things. folks like to mention that they trained hard, but have not heard of folks mentioned training smart.
Just want to mention that Aikido Journal has a good article on safe training practices http://blog.aikidojournal.com/2012/07/
and there is another good one written by Gev Nagiba on the same topic about the importance on sanshin.