If you ask someone involved in the court system, they will tell you that plea deals are actually vital within the current court system. The judiciary is, in general, so underfunded in many jurisdictions that it would be simply impossible to try every case. Plea deals lessen the burden on the courts.

Obviously, this shouldn't be seen as a defense of plea deals, merely an explanation of one of the incentives that currently exist for them.

Properly funding our court systems would remove this incentive.