It’s hard to argue those systems are not useful if implemented properly. Yes it can lead to prejudice if done improperly, and some prejudice is unavoidable (the whole point of the review is to do a lot prejudging for you to save time) to save on time and effort.
Those are reviews of businesses and products, not individuals. It's not equivalent.
But I’d give you a chance first.
The fact that people are rushing to downvote me for voicing a contrary opinion (and emboldening others to disagree and downvoting me too) is the exact embodiment of what I just described. Like it or not, human beings don't like outsiders and people that others dislike
Especially in the context of cultural production. We wouldn't have the Beatles ("more popular than Jesus" controversy, drugs, bed-in for peace) or probably any other rock/punk related music... also anti-racism, LGBT rights, feminism, and other social movements we look back on as positive would all have significant impediment to making progress if possible at all.
In a very narrow per-use-case context like rating a contractor on quality of work, or restaurants on quality it's obviously not a problem but the key difference is social-wide aggregation and enforcement of norms that sound good at the time (to a critical mass of people) but leave no room for society to evolve and improve through new ideas and beliefs.
Growing up in a racist area and taking a public stand against racism would give one a very poor score, even after leaving.
What you said you'd find helpful is a "global database of opinions" whereas being down-voted on this particular site is a very limited context.
Would you find it helpful if I happened to be in the key interviewer for a job that you really want and are fully qualified for and reject you based on my perception of you here, bubbling up through data processing and aggregation into a "global" system that's totally opaque to you? And further, that my negative reaction adds more data and pushes your score down?
Up/Down voting comments here is totally appropriate as limited to this context. Applying that type of data, invisibly aggregated across all aspects of your life is what's seen as a problem, correctly in my view.
Why? Many people hold many opinions about me, almost all of which are wrong. I don't see the value in a global database of opinions about me which I can't control and which will affect me in ways I can't predict.