His argument was when dog handlers have families, they often don't want to take the risk around young children and if the handler doesn't rehome then there isn't a place for them.
I've not known any to be destroyed after they retire. My GSD was amazing, both when he was at work, and when he was at home. He was such an awesome pet.
Family friends have all kept theirs after retirement too. Some have different ways of keeping them. For the most part, ours was kept in the house even when it was active. Some people keep theirs outside even after retirement. But I've not known any to be given up or destroyed after the retirement, as the handlers work so closely with them, for such long periods of time, they're awesome colleagues, and they eventually become part of the family.
It is an animal with a bite that can crush your bones. If it gets hold of any part of your body with its teeth you will be in far too much pain/shock to be fighting it. If you are strong/quick enough to grab a fully grown attacking Alsation and 'wring its neck' you should be wearing an S on your chest and saving the planet. 
. Don't they do it though because it helps their stomach? Our cats seem to it for that reason, still chunder everywhere though.
(Stuff like this: