In other words: these rules need to be explicitly stated in whatever contract consumer and provider agreed on.

These rules also need to be universally enforced. Rules that are (intentionally or not) written in such a way that they lend themselves for arbitrary application (that is, not equally amongst all consumers) are legally unenforcible. Therefore should be considered null and void. Which then leaves the service provider without any legal justification for their actions under contract law. That's at least how it works in many places, at least outside the USA.

If you want to limit the ways your service (or product) can be used, you can do so by explicitly arranging these limitations through a contract. Things that are already (otherwise) illegal do not have to be included in this arrangement (hopefully for obvious reasons).

Whatever is not explicitly forbidden by either law or contract, are not valid grounds for treating consumers differently.

Sadly, and mostly for historical and cultural reasons (and law enforcers not paying attention for a long time), it is often assumed that these rules do not apply to big service providers (and software producers alike). However, I have never found any legal basis for why such companies should be treated any different than any other one.