Its the principle, religious attire or not, its something which some could feel threatened by. Hiding your face in public is wrong, and if it offends people so badly, they should move to where its accepted and promoted such as saudi arabia, or any other Islamic state. Theres certainly plenty to choose from.
The fact is, if the whole of the population aren't abel to walk around with their faces covered, why should 0.01% of them be able to? They're not above the law, and its right that it should be enforced.