As far as I'm concerned, if you fly single seat then its your life and therefore your decision. I was always more comfortable being unstrapped on the taxi back and would justify that by saying it was quicker to egress if there was some kind of problem, but then again I didn't taxi out unstrapped.
In a two seat jet its a crew decision. Of course, when the canopy is down its not always appropriate to arm seats as the aircraft may be in a HAS or shelter.
Aircrew are clever people and spend years in training and IMHO are treated like children now by an organisation that seems to want to have a rule and procedure for everything.