LEXINGTON, Mass.—For weeks, high school debater Benjamin Waldman rehearsed his argument affirming the resolution that the criminal-justice system should abolish plea bargaining. Now that it was time to speak, he took a deep breath and let it rip.

“...thecriminaljusticesystemisareflectionofandapplicationofthelawandimpositionofpunishments.Pleabargainingwasamechanismforthesejudgestomaintaintheirvastpoweranddiscretion…”

After...