Free speech laws aren't meant to protect harmful medical practices
Conversion therapy is not only ineffective, it is also often harmful, especially when youth are pressured into it.
Even for adults, the essence of offering conversion therapy involves something very close to a fraudulent practice in that it promises something (the ability to change one's sexual orientationv via therapy) that the practitioner is not able to deliver. For both youth and adults, this not only wastes time and resources, it also stigmatizes an innate orientation.
In brief, there is no good rationale for allowing a harmful medical/therapy practice to occur in Virginia. Banning it is no different than banning any other discredited practice.