I am an American, and I agree our system is not perfect. There are sentence disparities, and the rich can frequently buy their way out of trouble. Also we have people in positions of power who are racists, sexists, homophobes, and fanatics. And we have Trump.
But, we have one thing going for us -- freedom of the press. You hear about the bad things that happen because our press can report it immediately. They can film and show interviews and they can report court proceedings. Injustices are made public! That's how you hear about them here.
Not to point fingers, but I have read terrible stories of UK children taken from the parents, put in foster homes and adopted out without the parents having the option of a lawyer, and without giving biological relatives the opportunity to take kindred custody. The UK press is not allowed to cover these stories until everything is a "done deal" and the parents have no appeal.
Also, yes there are too many guns in the US, but there are lots of knifings in the UK. We all could be a bit more civilized.