What Johnson actually said, (the bits ignored by detractors)
"So I was a bit surprised to see that on August 1 the Danes joined several other European countries – France, Germany, Austria, Belgium – in imposing a ban on the niqab and the burka – those items of Muslim head-gear that obscure the female face. Already a fine of 1000 kroner – about £120 – has been imposed on a 28-year-old woman seen wearing a niqab in a shopping centre in the north eastern town of Horsholm. A scuffle broke out as someone tried to rip it off her head. There have been demonstrations, on both sides of the argument. What has happened, you may ask, to the Danish spirit of live and let live?"

"I am against a total ban because it is inevitably construed – rightly or wrongly – as being intended to make some point about Islam. If you go for a total ban, you play into the hands of those who want to politicise and dramatise the so-called clash of civilisations; and you fan the flames of grievance. "
https://www.telegraph.co.uk/news/2018/08/05/denmark-has-got-wrong-yes-burka-oppressive-ridiculous-still/