Narrowly, you're right: the problem is sentence length, not plea bargaining. But broadly, causality doesn't run that way: states overwhelmingly prefer plea bargains on many levels (DAs want high conviction rates, states want few trials, etc.), so harsh maximum sentences are implemented primarily as a threat to help encourage plea bargains.
Even on a too-crude statistical level we can see the problem: if an innocent person has a 20% chance of being convicted, but the offered plea bargain is 1 year and the maximum sentence is 10 years, innocent people will do better by pleading guilty. The "10 years" is a problem, but it's a consequence of wanting to drive plea bargains.
(The fundamental problem in this case is the 20% chance, but frankly no one seems to have any hope for a system that doesn't regularly convict innocents.)
Yes, states -- and the society in general -- should have a slight preference against going to trial. Trials cost resources, and it makes sense for the body politic to compensate defendants who are willing to save society the expense of a trial that they expect to result in a guilty verdict anyway.
This is why most societies allow guilty pleas in the first place!
A plea bargain is nothing but a guilty plea + certainty about the sentence. If you're okay with guilty pleas but not plea bargains, then you think the introduction of certainty in the sentence makes it somehow worse. That's hard to justify.
I reiterate that the focus on the "plea bargain" part of this whole thing seems misplaced. If anything, it's the part that makes sense; the problem is the high penalties and bad-faith charges, which is what should be penalized.
>if an innocent person has a 20% chance of being convicted, but the offered plea bargain is 1 year and the maximum sentence is 10 years, innocent people will do better by pleading guilty. The "10 years" is a problem, but it's a consequence of wanting to drive plea bargains.
>(The fundamental problem in this case is the 20% chance,
That sounds more like tilting against the windmill of "variance in extreme events". We also have the problem that there's a 1% chance of being in a car accident with tens of thousands of dollars in costs. In most cases, we shrug and say "insure it" -- i.e. trade a small probability of extreme loss for a guaranteed smaller one. Why do we see it as suddenly a problem when people do the same thing in the justice system?
Every legit example of it being a catastrophe turns out to draw its entire badness from some other already-bad part of the justice system, not the plea bargaining.
Even on a too-crude statistical level we can see the problem: if an innocent person has a 20% chance of being convicted, but the offered plea bargain is 1 year and the maximum sentence is 10 years, innocent people will do better by pleading guilty. The "10 years" is a problem, but it's a consequence of wanting to drive plea bargains.
(The fundamental problem in this case is the 20% chance, but frankly no one seems to have any hope for a system that doesn't regularly convict innocents.)