I don't see nothing wrong with it. How can pretending to be a bride be so wrong and yet its ok to dress up as a witch, slayer or some horror flick character? Id you don't want your daughter dressing up like that then don't buy it but why force others to not have access to it either?
If that is so bad then they really need to look at a bunch of other costumes that may be inappropriate as well. Fact is there is nothing wrong with a wedding dress as a costume!