Plea bargains should not be allowed. Rewarding someone for not going to trial is equivalent to punishing them for insisting on their ancient legal right to a fair trial. If the prosecution wants to make a deal with someone in exchange for testimony then they can request a lighter sentence after the defendant is found guilty, but they should still be required to prove guilt.

Yes, I know the legal system doesn’t have anywhere near enough resources to take every case to trial. Don’t care. Give the system more resources or prosecute fewer people or some combination of the two.