A Claim to Authority
An opinion on something only matters if the holder has direct experience on the subject. A lot of times, “they” is used as a proxy for “people who are experts.” Who are these people? Many times, especially in politics “The People” is used to justify things, when that’s a very vague group, and are The People well-versed in the subject? Even if they agree or disagree, are The People experts in what’s being discussed?
Examples
Someone trying to make a point might constantly say “they,” as in, “well, you know they say…” Who “they” actually is, is never defined.
As President, Donald Trump had the habit of claiming that “many people are saying so” or “many people think.”