It doesn’t. Someone with a “left” view and a “right” view can cancel each other out,

Only if the person with a left view also has a right view. And only if the other person with the right view has a left view.

You seem confused. The point of it isn't to give a fully accurate explanation of a person's views on every topic. It's to give somebody a general idea.

Plus, someone can say they are for something, but actually not support it in reality.

All political measurements fall victim to that. It's a moot point. But just because some people are like that doesn't mean everyone is.