If this were true, then pushing the shoulder back in other high pressure cartridges wouldn't be a common practice--and it is. Same goes for fire forming brass, and wildcat alterations of one brass into another--all of which is done very regularly. It doesn't hurt anything other than work-hardening the brass over time. It will become brittle after a while, but debulging is nothing new or dangerous. Do what you like with your brass--just don't keep propagating bad information based on personal opinion.
Thanks.