No one is saying transition is a "regrettable outcome".
What people are saying is that some people may think they are trans and then change their minds later. In these cases a watchful-waiting approach is better because it may allow the person to avoid life-altering decisions like surgery or hormone replacement. This is not a hypothetical, there are recorded examples of young adults who, having undergone these therapies, came to regret it later.
> You are the company you keep.
If we extend this logic (which we should under no circumstances do) we could say that Aimee Challenor is guilty of the rape and torture of a 10 year old child.