There are plenty of things that you could do 'on the sly' that are illegal. That's doesn't mean they're not illegal, and that doesn't mean that if you are found out (which is hard but not always impossible) that you will be punished. Given that there are plenty of legal ways of making money, why would you pick an illegal one just because you (think you) can?

The boundaries of the law are rarely set at what you think you can get away with, but are usually set on some other principle and in between that line and the point where you exist there is plenty of room for prosecution. The jails contain lots of people who thought they 'could get away with it'. Don't be one of those.

At ~$150k per willfully-infringed work, infringement at scale gets expensive real quick.

Do you feel lucky? What if a specific version of Stable Diffusion is found to be infringing and there's a way to back-attribute an image to it?

https://www.law.cornell.edu/uscode/text/17/504