Just against an ogre friend of mine who wanted to try out his aikido techniques on me. He strained my wrist (both already broken before) because I was stupid enough to trust him not to.

Response to comment [from a Christian]: "Aikido is the only martial art that deals with an opponent without harming them."

We don't harm individuals when we train.

White belts can be tricky to train with because they don't move in predictable ways.

Everyone has a survival ability.

Response to comment [from other]: "Spitfire I have practiced a lot of the nerve strikes taught in ninjitsu and like you say, unless you live and train it like in kill bill it wont work to well..."

Haven't seen the movie. One of our senseis has a yearly camp where men stun gun themselves and expose themselves to a variety of harmful things to ensure that they can continue to fight under extreme circumstances. I don't personally stun gun myself. I think it'd probably knock me out and I'd unlikely get up anytime soon.

"...[Y]es when you hit them they will shut down the nervous system but if you miss you would have been better of with a good palm to the nose to stop them from seeing and make your getaway..."

Certain strikes to a particular area of the leg for example can collapse an individual. We learn to attack bones, muscles, airways, etc. The same nerves and muscles we attack can be soothed when we are under no threat level--depends on whether you are friend or foe.

Response to comment [from a Christian]: "Whether or not someone is harmed, we should accept the truth that if our intention is not to harm, sometimes the effect of our good intentions DOES harm someone else. In that case, we definitely have harmed somewhat."

That happens all of the time.  It's not ballet.  I don't harm others when I train.  If I get harmed, it's my own fault.

"We have to be accepting, flexible and nimble whenever we encounter conflict. This means that instead of taking shelter in either giving in or fighting back, we should take advantage of the many other choices available to respond to conflict in more useful ways."

There is no end to learning.  You can start young or old; you can jump in at any time and at any age.  One man I trained with was a stoke victim.  One side of his body was good for nothing but the other side of his body was like Popeye the sailor man!

[Everyone has a survival ability] "I agree. It might not be evident, but it can be brought out and encouraged when others do not use it or acknowledge it."

Women in particular should take martial arts.  Both of my kids trained. 

The more years of training you have, the lease likely you are to have to use it by the way. 

Response to comment [from a Christian]: "Best defense:

Here, here. Sell sword, buy gun (Lk 22:36).