I agree with both halves of what you say.
An added flaw is that, by banning conversion therapy only for people under 18, the law interferes with parents' rights to raise their children. The only similar law is in California, and it is being challenged in court on that basis.
Indeed. Even though "conversion therapy" is basically quackery from a medical/psychiatric perspective, parents should have the right to take their children to quacks, except perhaps in life-threatening situations (I suppose a line should be drawn for those who would take their children to a faith healer when they're dying of sepsis that could be easily cured with antibiotics - the logic being that you can make yourself a martyr for your beliefs, but don't make your kid one).