> I reject this idea, someone voting for the "least worst candidate" does not wholly endorse everything they stand for

The thing about values is that they don't just capture the notion of what we thing is right or wrong, but also which things we value over other things. In an extreme case, two people can agree on 10 out of 10 different ideals or ethical stances and still have different values and support different parties because of how they rank those things.

In that case who you think is the "least worst" is also a reflection of values, as is declaring both sides to be the same, or opting out altogether. They all represent both what things you value and how much you value them.