Decocking when dismounting is essentially what I was taught in defensive training long ago. Since then I've seen a lot of people do a lot of moving around with a DA/SA gun in SA mode in a competitive context. That prompts me to think more about the defensive doctrine of decocking, though that is still what I would go with. And since no one seems to have brought it up yet - what about an SFA without manual safety? A lot of those guns have triggers that are approximate to a lot of SA triggers, with some extra slack in the front. Obviously, there is no option to decock them, but would we in the defensive world consider it unsafe to move with an SFA in hand? We clearly don't. So that gives me more pause on the defensive doctrine of decocking and prompts me to think about it some more, though that is still what I would go with.
Just a few more thoughts for the discussion!