No, an artist absolutely should have a reasonable expectation that their improv at a coffee shop won't be ripped off next week by a billion dollar publisher.

> Don't share it with them until they sign.

Which would be possible in a situation where someone has the power to do so, but this isn't always the case. In industries where there are large negotiating power imbalances between creators and others they work with, you will typically find that creators have little to no negotiation power. There's a reason we have many legal protections in many parts of the law outside of contract law.

> If you don't trust your spouse then get a prenup. The other categories aren't special.

A spouse is the most formal of the examples I listed. And a spouse in many places is someone you've already entered into a formal legal agreement with. But to the contrary, I don't think it is reasonable to expect people bring NDAs to a first date.

> That said, if your work is so easy to copy it probably wasn't (or shouldn't have been) valuable to begin with. Implementation matters more than ideas. So most of these concerns are silly to me.

The concept of privacy isn't predicated on monetary value.