Because right now, millions of women are both legally and\or socially treated as second class citizens, with that "clothing" used as a tool and symbol of that oppression.

I MIGHT accept your assertion that the veils of the Gulf States or the burkas of Afghanistan are symbols of the oppression of women, but I do not accept that head scarves are the same. I am unconvinced that Islamic women in much of the world (outside of those areas mentioned) are appreciably more oppressed than are women in other societies of similar levels of economic development.

A Hijab and Niqab are a form of mask, designed to protect against people seeing you.

But we are not talking about niqab (burka) here, we are talking about a headscarf, which covers (incompletely at that) the woman's hair, not her face.