When the State charges someone with really heavy charges and then bargains down with the defendant that's clearly wrong. If a person has in fact done really heavy stuff, then he should have to answer for it, all of it. Either the State can prove its case in its entirety or it shouldn't bring it. RICO is a prime example that is clearly malevolently misused by prosecutors to coerce behavior. Bad Law for good reasons.
Defense attorneys do the same thing on a different front.
They have the defendant routinely plead Not Guilty regardless of whether or not he did the deed or not. The reasoning here is to delay the process for as long as possible in the hopes of wearing down the prosecution to get a better deal for the client. Witnesses die, move, disappear. Evidence gets lost. Other things get more important for the state to pursue.