If you have ever seen a person who is mentally ill then you know they cannot speak or think correctly so how could Boo ever present himself in court. He just wouldn’t do well if put in this situation. And also how would Boo do this if he can’t speak and he was the only witness.
Although it is not right to lie, sheriff Tate did this to protect one of his people. And Boo may not get the credit or recognition for protecting the kids, but he will always be a hero to Scout and Jim. I believe I would do the same thing in Sheriff Tate’s situation so yes I agree with his decision to help