This is naive.

You are arrested for a crime you didn't commit. The prosecution charges you with a serious crime with punishment of years in prison. Your lawyer can't guarantee you'll be found not guilty and you'll be in jail for a least a year until the trial because you can't make bail. The DA then offers a plea bargain to a lessor crime with several months in prison.

Lots of innocent people would, and do, plead guilty to the lessor crime.