Yeah in general it's not a problem to anyone, same as youths wearing hoodies isn't.
It's just in the event of a crime it makes it incredibly difficult to identify them (you don't see hair colour, distinctive facial features or scarring etc.). It's against the law (or something) to wear your hood up in a store for this reason, yet it's not against the law to wear a Burka, despite it covering even more than a hood does.
It's basically allowed most places because politicians have no balls and are afraid to do anything that could be construed as "against Muslims" and thus be branded as racist and become the target of abuse and such. But what in fact results is double standards... so you get an increased amount of people showing disrespect for Muslims because they're able to get away with all this shit and they aren't even in their own country.
It's lots of little things like this that make small questionable parties such as the BNP grow because more people side with them when stuff like this is topical.