Mislabeling can happen, but that alone doesn't invalidate the usefulness of the term conspiracy theory. Science can be (and by default, often is) wrong. Some things might genuinely rely on weak or un-falsifiable reasoning. For now.
Every era creates its own intellectual blind spots. We don't know which of today’s dismissed ideas will later look more like actual history.
I don't argue that dismissed ideas are secretly correct. But labels do influence how seriously we investigate them.