Freedom to seek (legitimate) medical needs without government interference is an important freedom. But when harmful practices charade as "medical care" it is the governing bodies' responsibility to step in and restrict/prevent them from taking advantage of the public's trust in "medical" services.
Conversion "Therapy" uses the harmful practices of rejection, shame, and psychological abuse to force young people to try and change who they are. This is an affront to all true therapy professionals whose aim is to provide evidence-based care, validated to treat legitimate disorders and deficits, in order to improve the long term outcomes and quality of life for the patient.
Banning 'conversion therapy' is an important step in helping the public avoid being victimized by dangerous and harmful practices and increase the likelihood that those who do in fact need professional help will seek the help they need from qualified providers who utilize evidence based care.