Common knee jerk reaction with aggression rehabilitation

I have seen so many aggressive dogs who were totally healthy that were sent to various vets for all sorts of tests - when what they had was a behaviour problem that is not going to be detected by MRI, CT scan, X ray or things like that.

When nothing was found by these so called experts, instead of finally suggesting the owners to send their dogs for some proper training, they would suggest euthanasia!

Have they ever considered the followings:

If a dog had a tumor in the brain that is causing him to become aggressive, why wouldn’t such a dog attack me, my wife and my children?

If a dog had some hidden pain that is causing him to bite whoever touches him, why is it that he is totally fine with being touched by me, my wife, and my children?

If this dog attacks other dogs because of some hormone issues, why wouldn’t this dog attack other dogs when he is living with me?

If it was a medical or health issue, why does it suddenly disappear without any medication or medical treatment once he is living with me?

We have seen many dogs who became very good dogs after they finished their trainings.

If they can be successfully transformed with no medical treatment, how could their problems be medical?

Why don’t we give these dogs a second chance by providing them with proper training instead?