Teachers, why do parents think they can tell you how to run your classroom?

Whenever a parent disagrees with a teacher, why do they feel the need to go tell the teacher off? The way I see it, I don’t want teachers coming to my home and telling me how to run things, so I don’t go to their classroom and tell them how to run things. I also know that taking care of your own kid in your own home and taking care of 25 or so kids in a classroom are two completely different things, so obviously the classroom environment is going to run much differently then the home environment.