I know they are something that most of the American population (girls included) either like or don't mind (and I am aware that not all men like them, merely the vast majority). There are a lot of such things in society like this. For example, most of Americans like handcuffs too. o.o Something just awesome about being restrained. What about high heels? A lot of women feel sexier in them and a lot of men think women look sexier in them.
I guess I'm just doing a case study in what kinds of things in society that have become sexual symbols? A SYMBOL is defined as something that represents an idea or thing completely unassociated with the object. Now, you may protest that under the definition lesbians don't count, but I say they do. Nothing sexual about sexual orientation. I think...
(further evidence of this can be noted if you think about WHY you entered this thread)
Anyway, what can you think of? It's odd the way a society can take a cultural resource and add deeper meanings.