Conflicting terminal values are very much possible. I don't think they exist to a relevant degree among humans.

What exactly do you think is happening in disputes about legal interpretation or legal change?

I'm not saying that every such dispute is caused by value differences, but a substantial number are - and there is a strong social taboo against articulating disputes in the language of value conflict. The socially preferred method of argument is to assert that "common values" support the result that one prefers.