They should make it clear during hiring if you will be expected to be on call. Whatever is agreed upon is agreed upon, but enough of this cowardly, entitled scope creep. Have the nads to tell prospective employees up front what will be expected of them and accept the likelihood that they will either ask for more money to do that work or refuse outright.

I’d like to live in a world where it is usually expected that when you leave work your time is your own.

But I don’t think this is an inherent right. Your right is to enter agreements voluntarily, nothing more.