What is the objection to a law against something that we're told no one is doing anyway?

I'm reading "Tennessee Bans Hormone Treatments for Transgender Children/The measure signed by Gov. Bill Lee makes it illegal to give prepubescent minors the gender-confirming treatments — a practice some experts have said is not in use" (NYT). 

If medical practice already draws the line in the same place — no hormone treatment before puberty — then why object to the law? Or you can put the question the other way: Why pass the law?

1. There is symbolism — messaging — in passing the law and in refraining from passing the law. Politicians might want to express opposition to/support for transgender people.

2. There is trust/mistrust in the medical profession. Do you believe they'll determine the best treatments and restrain themselves from going too far, or do you think they need a legal line? The AMA position is that the law a "dangerous intrusion into the practice of medicine."

3. Regardless of what the medical profession decides is ethical, there are always unethical practitioners, and you need a law if you want the government to impose consequences. If no one ever violates the law, it may be because the law deterred them (and not merely that every single practitioner hewed to the ethics). 

4. How strong is the evidence that no practitioners give hormone blockers to prepubescent children? Advocates make assertions, but how do they know? The article quotes 2 advocates, but each only said that he's not aware of any practitioner who gives this treatment.