Is the problem not about who and how said it? Surely in his political rôle he should indeed be careful what he says and how he says it?
I personally, as someone who has many Muslim friends and family, think the burka or full face covering should be banned, simply and clearly, in public places, in the UK and the EU. Allow full length clothing and sleeves, allow a scarf, even if it covers side of face, as long as face/eyes are not covered. Some of my Muslim family and friends totally agree with this too.
But for Boris Johnson to officially write such words in the Press, is totally unacceptable and offensive- and no gaff but totally calculated for effect.