Someone about to commit a terrorist act - plant a bomb, or wear a bomb and blow himself up - is going for inconspicuous. Yes, occasionally a terrorist in the Middle East, where burkha-clad women are everywhere, might disguise himself that way, but in the Western world he's going to want to blend in until the last possible moment. This has nothing whatsoever to do with security, and everything to do with cultural and religious bigotry.
As for wanting to "liberate" women from the assumed patriarchal oppression of their husbands and other male relatives, a law like this will result in exactly one thing for women in that situation: they won't be permitted outside the home at all.