What guilty person?
We don't have guilty people before a trial. Even if they admit to it, they're not guilty until the trial. That's central and fundamental to our system. Otherwise you have a justice system based on proving a negative. Want an example of why that's bad? Last week your neighbor lent you his lawnmower. Last night you got into an argument about a dog. Today the police show up - your neighbor says that you stole the lawnmower! Now, kindly provide evidence that you didn't steal the lawnmower. You can't prove the negative? You're guilty - go to jail. Thankfully, that's not how it works. The neighbor says you did something wrong, and it is up to him (or others, on his behalf) to prove it. If there is no proof one way or the other, you're innocent. You're innocent until someone proves you're guilty.
What we do get is people who falsely confess to crimes to protect someone else. What we do get is innocent people charged with crimes due to any number of flaws in the system (especially eyewitnesses, but also prosecutorial misconduct, evidence errors, etc) What we do get are people who plead guilty because of threats. What we do get is extenuating circumstances - not every theft, not every murder, is identical, but when those factors are in the favor of the accused, who stands up for them?
Does defending the genuinely known guilty suck? Yeah, a lot, and for a lot of defenders it is genuinely traumatic. But if they didn't do that, it would be somebody other than the courts that would be deciding that people accused of crimes were guilty, without a trial, without evidence being presented. That can't happen. Ever.
Sometimes the system protects terrible people, but getting rid of those laws would also be getting rid of the laws that protect the falsely accused.
