There is a line between the judging that you're doing and the judging you say is deserved.
As you said, people can dress themselves. They can do this as they please with scant or no regard for what others may think such is the society we live in.
In your profile picture you appear to be wearing a t-shirt and shorts in public. So you think sagging is stupid, I'm sure those of an older (undefined age ) generation think you look scruffy and under dressed for being out in public because you're not wearing a shirt, tie, smart shoes and smart trousers.
Victorian gentlemen wore a suit, top hat and all of the above when in public.
As for your assertion that allowing her children to dress as they choose is bad parenting and that obviously the cousin is craving affection because he dresses as he pleases.. Oh. My. God.. What an awful, bigoted, sanctimonious, holier-than-thou opinion to hold. Grow Up.