One of the things that is really weird about this ban is the fact that it is so specific. If there really is a problem with therapists pushing to change people's self-concept and/or lifestyles then surely this needs to be tackled on a more generalised basis? Sexuality and trans-identification can't be the only arenas where any kind of therapist-led change is potentially damaging/intolerant/ideological/disrespectful.
What about the cases where parents arrange therapy for their adolescent children with a view to 'correcting' what the parents see as a problematically rebellious lifestyle -- partying, not studying, having a lot of sexual partners, abandoning the parents' faith, etc. Why are these types of therapy less in need of a specific ban?
The reality is that any form of therapy that is perceived from the outset as geared towards changing the client in a pre-defined way needs interrogating.
Even when the change is easily recognisable as something constructive that the client has rationally and autonomously sought: Say somneone begins therapy with the goal of improving their self-esteem or moving away from disordered eating, it is still the therapists' professional duty to review that goal continuously - maybe it is a screen for some deeper, more troubling issue, or perhaps it is not an authentic self-determined goal but just something the client's family framed as a problem, etc. The therapist has to be led by the client's self-exploration at all times, and to interrogate their evolving priorities, rather than uncritically pursuing what seems to her a highly obvious unquestionable good outcome.
And of course there are loads of potential changes that a client might be seeking through therapy that are in a grey area -- not obviously good or bad, not obviously helpful or unhelpful for the client. No therapist should accept these as the pre-defined goal of therapy. The goal should be constantly reviewed, and possibly dismissed, in the light of whatever the client brings to therapy.
In other words, you would pretty much have to be an incompetent and/or authoritarian therapist to be pushing for any pre-defined change in the client. So legislation, if any is needed, should probably be aimed at tightening up who can actually market themselves as therapists. Most relevant words relating to providing therapy aren't 'protected' and anyone can use them to promote their services. So we should probably start by defining standards that must be met in order to be authorised to promote oneself as a therapist