(1) Had defendants refused to settle, many of them would not have been charged or would have escaped with lenient sanctions.I don't see how refusing to settle would get a defendant "lenient sanctions", except for a not guilty finding. In general, one would expect a pragmatic prosecutor to offer a better deal than Defendant could expect to get even if Defendant just pled straight guilty and got a disposition from the judge. I'm not saying Prosecutor will give up the farm, and she won't offer a punishment which is insufficient, but she'll offer something at least a little less than what the judge will probably hand down. Of course, there will be exceptions to this - charges which cannot garner an offer, judges who are too lenient for a prosecutor to conscientiously make a better offer, the rare unreasonable prosecutor - but this would be the general rule.
On the other hand, if somehow all defendants, and their attorneys, decided that from a date certain there would be no more plea bargains and that they were all going to plead not guilty to everything it would benefit a number of defendants in the future. Of course, the first group to do this would have a lot of people who would get longer sentences than they would have otherwise, but, assuming the government could not increase its resource expenditure to handle all the cases, the government would eventually have to bring fewer charges or drop more. This would benefit those with lesser charges. However, those with more serious charges are going to see the time they spend in prison increase.
As a practical matter, you'll never see all the defendants act in concert. In the short run it is to most of their self interests to take the plea offer. As well, defense counsel isn't charged with defending the best interest of the group, he's charged with defending the interests of the single defendant in his care. He cannot ethically recommend Defendant take one for the team and spend a year in jail for snipe hunting (instead of the 9 months offered) just so that someone else might not have to be charged or convicted of this crime in the future.
(2) The substantial bargaining power of the resource-constrained prosecutor is therefore the product of the collective action problem that plagues defendants.Yes, this is partially true. However, that's an incomplete picture. A good portion of the power in a prosecutor's hands comes from the fact that a large percentage of defendants are provably guilty. They've been found by an officer in possession of contraband. They shoplifted while store security was filming them. They confessed to an investigator. Let's say that these "easy proves" are 60%. In those cases the only real thing which is going on is a determination of what the disposition shall be. If Defendant and Counsel know Defendant has a 99% chance of being found guilty and getting 5 years from the judge, that is what gives the prosecutor a lot of power to plea bargain. The prosecutor has the power to offer anything up to a 5 year sentence. Then come the "probable proves"; let's say these are another 25% of the cases. In those everyone perceives an 80% chance of conviction and therefore Prosecutor's plea bargaining power is less; perhaps her power only rises to the level of the ability to offer up to a 4 years sentence. The scale continues to slide as the perceived ability of the prosecutor to prove a case lessens. Mind you, the plea bargaining power of a prosecutor never completely ceases to be; the mere existence of the ability under the law to offer a plea agreement assures the prosecutor will always have some power in plea negotiations. In a murder case which both sides perceive to have a 5% chance of conviction an offer to reduce to felony battery and probation (rather than potential life) is still something the defense is going to have to consider.
(3) [T]he institution of plea bargains may not improve the well-being of defendants.Since when is the purpose of anything in the courthouse meant to "improve the well-being of defendants?" Assuming Defendant's interest in court is that of self liberty, the only way he can achieve this in totality is to fight all the way to the end and be found not guilty. In a plea negotiation situation Defendant isn't trying to improve his well-being, he's trying to mitigate the harm society is going to inflict upon his liberty interest in order to further what it has decided are important ends.
(4) Thus, we can no longer count on the fact that plea bargains are entered voluntarily to argue that they are desirable for all parties involved.Were plea bargains ever entered "voluntarily?" Were they ever desirable for all involved? Let's be serious here. In a perfect universe every lawyer, prosecutor and defense, would have one case and all the time and resources in the world. Judges would be assigned one case at a time and have no docket pressure. Jurors would be bright, attentive, and take their duties seriously. There would be no reason for even a plea at the beginning of trial; we'd just assume a not guilty plea and have at it. In such a system defendants would probably benefit in that more of them would probably be found not guilty. The citizens would also benefit in that there would be no need for the government to discount sentences; those convicted would be segregated from society for as long as they optimally should be.
However, this isn't reality. Judges are coerced into plea agreements because they need to keep their dockets moving. Prosecutors are coerced into plea agreements because it is problematic to gather all the witnesses and all the evidence for each and every single case they are prosecuting, concern about witnesses/evidence, speedy trial concerns, &cetera. The defense is coerced into plea agreements because of the probable worse consequences if the agreement is not entered into. Sure, no one's free will is overborne, but it isn't exactly as though everyone gets there without some force within the judicial system pushing him in that direction.
Just as true is the fact that plea agreements aren't desirable for all involved. They turn the esteemed, legally brilliant judge into a clerk for the prosecutor and defense attorney who are basically just filing their agreement with him. The prosecutor generally offers less than she really thinks is the optimal punishment for the defendant. And what defendant desires his liberty interests to be imposed upon?
Yet, plea agreements aren't going away anytime soon. They are the oil which keeps the judicial system flowing and unless someone comes up with something better they're going to be with us for a long time.