Please do qualify that statement by acknowledging that there are a significant number of innocent persons who are convicted of crimes because they have accepted plea bargains for reasons that may have nothing to do with criminal activity.
I personally know of people that have accepted convictions for violent crimes who I know are not guilty of the crime. I know that they have done this to protect the victims of the crime, not some criminal.
Prosecutors are very skillful at negotiations for plea bargains, because it is the sole metric by which their performance is judged. They have access to secret surveillance. They use it to blackmail people every day, and get them to accept plea bargains.
I once asked the Assistant Deputy District Attorney acting as counsel for a Grand Jury investigating jails in the county I lived in that I was on, how he could sleep at night. I had knowledge of prisoners being sexually assaulted (they had told us, while standing right in front of the guards they were accusing, who also threatened retaliation openly), and had a private conversation with him where I ascertained he knew all about it.
He told me he slept in a big, expensive, comfortable bed.
A quarter of that Grand Jury had been beaten by police, but no one was willing to do anything about it. I tried, but I had young toddlers at home. Once you receive a credible threat against your children, it is difficult to sacrifice them - particularly in a system that will absorb your protest without even noticing - even if you know many other people will suffer.
My kids are no longer children, so I no longer am silent.