What is wrong with wearing a burqa?

Boris Johnson has once again got into hot water, and once again his comments have provoked furious reactions on both sides—agreeing and disagreeing with him—but I wonder how may actual read what Johnson said? It is worth reading (and worth the trouble of registering on the site) if only to know what it is that people are debating. The central line of his reasoning is that it seems to him paradoxical that in a country like Denmark, which appears to pride itself on a radical understanding of freedom that protects things we in the UK would find distinctly odd, the burqa is banned when that would be unthinkable here. 

But of course Johnson hasn’t simply offered an argument; he has offered an argument using his swashbuckling and confident style of writing, which makes it very interesting to read but also makes it easily offensive. The offending phrase came in the description of the perception of those wearing burqas in the UK: