I'm still of the opinion that the women who "choose" to wear these coverings do so because of, at the very least, peer pressure. Many of those defending their choice point to their dislike of fashion magazines, their criticism of women who "flaunt" themselves, etc. and even bring harm upon themselves because of their dress. So even women are involved in blaming women for violence against women.
As Ulfhedinn stated, however, there certainly are plenty of women who are forced into it. To get back to the original point of this topic, it is one factor which causes many of us to dislike islam (as we do and would any religion or rulings which force people into anything).
This one makes for an interesting read, including the comments afterward:
http://www.womenundersiegeproject.org/blog/entry/the-myth-of-how-the-hijab-protects-women-against-sexual-assault
Some more.
http://www.islam-watch.org/ma_khan/Living-Under-Sharia-Plight-of-Women-in-Saudi-Arabia.htm
http://www.yourmiddleeast.com/columns/article/video-iranian-womens-fight-against-the-hijab_13685