The simplest way to prevent the unions from seizing up and breaking when removing them is to smear brake grease on the threads and behind the unions making removal easier. There will always be reports of pipes splitting when trying to remove them, this is most likely due to people not assembling them with brake grease and they then split or break because they are seized. As for flattened pipes it is easy to have a careless moment and place a jack or stand in the wrong area (I think they are called senior moments
)
As for the plated steel pipes so called "rotting" one thing I have always done on my cars, modern or classic is to paint grease on the complete brake lines to aid against corrosion. This advice came from my father in law who spent all his working life as a mechanic and was a great believer in preventative maintance.
As les says though,there will always be two schools of thought.
