If an injustice is going to be committed I'd rather one that can be rectified, even if in an imperfect way. If you ban transgender women and it turns out there's no advantage, then that's that, we'll never know how they would've done. If you allow them to participate and we discover that indeed the advantage was what caused the win, you can rectify the results, like it happens in cycling all the time because of doping.
Imperfect, sure, but better than just banning while the jury is still out.
A year ago or so a transgender athlete here got some heat because of this issue. She ended up not winning anything. I suspect this will be the case for 99.9% of transgender athletes, they'll never win olympics or world championships. By the law of averages, some will eventually win, but maybe it's probably because they're better.
With so many questions up in the air, banning people as a preventative measure goes against the olympic spirit. The rules say participating is a human right, we should not deny any woman that.