I'll never just judge content based on its rating.

I'll argue that you do this all the time. For most people, they value the diagnosis they get from a doctor more than the diagnosis they get from their hypochondriac aunt. And this generally holds true even if you "don't like what was said". Imagine the doctor tells you that the chest pain you have is a sign of a serious heart condition and not just heartburn. You might not want to believe it, but you'll likely take it seriously, because you have some reason to respect the reputation of the information source.

The only way this can be useful is if a whole community uses the same algorithm, and the ratings appear the same for every user in the community.

In my opinion, that's the opposite of useful. For example, a system that doesn't at least allow for an initial diversity of opinion wouldn't allow for a proper exploration of the solution space needed when tackling scientific questions.

On the other hand, allowing for diversity of opinion doesn't mean that consensus can't emerge on the truth of many issues. I'm simply proposing ways we can use computers to improve the process we already use, and we've seen historically that most of humanity has over time been able to reach consensus on many topics.