Yes, it is a matter of safety.
Looks tell a lot where i am, a university student has not the same and attitude as a punk, a rascal, a military etc...
Looks sure prevent me from meeting cool people, but it also helps me avoid a LOT of dangerous people.
When there's a guy that's screaming in the crowd, talking to anyone telling their story all day, stinking so much you can smell them before you see them, you know you have to bail out because these are crazy/scrougers. Guys showing off their muscle, acting as "virile" as they can, like to compare with others via muscle, run because it's either a criminal or a military.
These are a few examples but it tells you how i keep myself safe in this piece of shit city. I've grow up between honest people (my friends) and this kind of people (my familiy's friends) and i really don't want to have anything to do with this kind of people.
Of course honest-looking people can be dangerous, but it's less likely that they directly threaten you health/life.
Never overestimate mankind.