“Why do you think the military makes soldiers march? Having a common group identity it’s always bad.”
Tell 100,000 civilian men to walk to a point 20 miles away in short time and be ready to present an organized fighting force almost immediately.
At the same time have 100,000 military men do the same thing (except marching), you might notice a difference in the result.
True, but the Navy also does a lot of marching as part of training, and will freely admit most sailors hardly ever march after they get out of boot camp. Police academies often do marching as well.
Marching does lead people to think of themselves as part of a group. This form of training can be used for good or ill.