I'm not sure what you mean by this. When counsel tell you something is legal, and it isn't, there's little subjectivity.
Stating that a thing is or is not legal is making a claim about the opinion other humans in positions of authority (whose specific identity is unknown) will have on a similar question in the future.
There is always subjectivity in it, since you are literally predicting someone else's subjective opinion. The objectivity of law is a conceit, not a reality.