I'd like this debate to mostly focus on the psychological aspects of plea bargaining on defendants, and not get bogged down in legal details.

Well, that's problematic, you see, because it suggests you're only interested in entertaining a certain kind of argument to change your mind.

I'm about to graduate law school. I worked as a prosecuting intern in a county attorney's office last year, and had a provisional license to practice law in that capacity. I handled simple misdemeanors, which are very minor crimes - usually traffic related, some public intoxication, minor theft, that sort of thing.

Let me tell you, working as a prosecutor is easy. The police do most of your investigation work for you, and you just need to establish the elements. It's true that every once in a while they get the wrong guy or arrest someone for something they shouldn't have, but seriously, like 99% of the time, the cops arrest guilty people.

For some reason it is assumed that the plea bargain will be a lesser punishment than that which a jury would give out, but there is no evidence for this.

Well, here's some. I'd routinely offer plea deals because I was too damned busy to deal with 15 trials per week, and it's expensive to pay officers overtime to come in and wait to testify for a few hours. If you got charged with three things, say, expired driver's license, expired registration, and no insurance, I'd offer to drop one or two of the charges in exchange for a guilty plea on the third, and recommend a minimum sentence to the court. The defendant who was completely (on tape admitting the charges) guilty would get only about $450 in fines from my plea deal, versus $1200 in fines from me taking the extra time out of my day I'd need to convict him. I'd do the same with certain crimes that involved jail time, such as violation of no-contact orders, so we're not talking about just fines. I'd do this week in, and week out, and I have many colleagues who did, and do, the same. Defendants routinely get a much better deal from plea bargains than they would have gotten later that same day had we moved forward to try their case.

The preceding paragraph is, believe it or not, "evidence." It's not admissible, and it's anecdotal, but it is evidence. It also happens to be true.