Doc was wrong on the starting point of Marty's downfall
He was convinced that the starting point was 2015 with the arrest of his son but,the starting point was clearly the car incident that destroyed his dream to be big in the music buisness. And as we notice in the final moments of BTTF 3,that incident was supposed to happen in 1985 (but a more mature Marty doesnt say yes to the challenge of those boys so he avoids the incident). So Doc created a big mess because he didnt understand the right starting point,but he ended up helping Marty to mature anyway.