That's a trope. In reality, the justice system is about striking a balance between the need to preserve order and security and the need to protect peoples' rights. That's why the Constitution uses "balance-y" words like "reasonable" when talking about 4th amendment rights.
> I don't trust your friends view of clearly guilty, sounds like bias to me.
I'm sorry to break it to you, but most people the police catch are "clearly guilty." Even my PD friends acknowledge that most of their clients are "clearly guilty" (they see their jobs as more watching out for the ones that aren't and making sure the ones that are get at least a proportionate punishment). The media likes to cover edge cases, but for every one of those, there are a dozens of people who rob a liquor store and leave video evidence of themselves doing it.
It is interesting to note that even most of the cases that are central to defining 4th amendment rights, ones where judges have come down in favor of the defendant, are nonetheless ones where the defendant did actually commit the crime he was accused of committing. Ernesto Miranda was convicted the second time around, for rape, even with his confession excluded, served time, and was ultimately killed in a bar fight.