That's because you still have to account the innocent people who are wrongfully convicted. There are many reasons why they're wrongfully convicted. There might be corrupt police, tampered evidence, influential families, terrible defense lawyers, unreasonable judges, racially-charged accusations, emotional juries, and many more. Those may end up having innocent man behind the bars, or worse, inside the noose. Even if they pleaded guilty, there are factors that they did that. Maybe financial constraints, early societal judgment from social media, peer pressure from estranged family members, etc.
Wrongfully convicted or not, they should get to choose where they're headed. Who is 100% sure that this man is guilty beyond reasonable doubt even if the courts get it wrong?