Good for him for suing.
I think "Conversion Therapy" is stupid. I also think 90% of the way Islam/Christianity/Paganism/whatnot is practiced is stupid. I also think 99% of what people watch on TV is so vacuous as to make the word "stupid" seem like a compliment.
I also think believing stupid things and practicing stupid beliefs and raising your children to believe and practice the same stupid things is necessary in the pursuit of liberty. Now, if your goal is to engineer some kind of Utopia, then naturally you will need to place liberty farther down the priority list in order to make sure everyone pulls in the same direction toward your idea of Utopia. Get ready to spend all your time writing every more specific and byzantine laws to make sure congenitally stupid humanity doesn't keep doing more stupid stuff. Which is a pretty good description of California, particularly the statute in question.