Asymmetric fields are in a temporary transition state to/from required. So it would seem a bit odd to me for the transition state to be the default.
However, I think I see your reasoning: you don't want to accidentally introduce a required field without first making it asymmetric, and having asymmetric as the default would effectively prevent that.
However, I think I see your reasoning: you don't want to accidentally introduce a required field without first making it asymmetric, and having asymmetric as the default would effectively prevent that.
So I can see the appeal of both designs!