AI products are rarely running locally. You're using the service of a company, who is not doing so for free. Even if you aren't paying, you're consuming the product. Like you said, they can regulate sales, like this.

I agree, it's practically unenforceable (on the consumer). However, there are many such laws. They're usually used to add on to a crime that is already committed. Rarely does someone get pulled over for not wearing a seatbelt, for example.

They do not have the right to create a law that infringes on your personal rights to access legal content.

It's not legal content if they make it illegal. For example, like you said, they can do porn bans, right? If they restrict accessing AI products, that's the same thing, right?