I hate the name. Very American and prudish sounding.
That said, they are a solution for girls who want to wear a dress and who do not want people to see their underwear.
I don't think it's sufficient to say "Well, they should all just wear trousers all the time" or "What does it matter if their underwear is on display"---I'd be delighted for girls to have the option of trousers/shorts for all school uniforms and so on, but what if some girls choose to wear skirts or dresses? What if the preference not to show underwear is coming from them?