Didn't read the responses at Kos, but in a sociology course I took on deviant organizational behavior, we learned that shocking/hurting someone as part of their training RAISED the likelihood that they would then go on to harm/shock persons in their care.

You are desensitizing them in many ways.  The standard way the taser training is done doesn't help either.  A police recruit is tased, but in front of all the other recruits, so that an "it was nothing" macho front had to be kept up.  

It also brings an air of superiority to the taserer over the taseree.  "I withstood this and could handle the pain.  You cannot, therefore you are weak and worthless.  Unlike me."

The most effective thing I've found to say to people is that a judge wouldn't be allowed to sentence a child molester to being tased as punishment.  Why are police allowed to tase anyone they want without oversight or accountability?

Note: this issue is very personal for me.  My husband has a seizure disorder and has been beaten by the police and almost shot for basically staggering around and drooling.