What oliversmumsarmy is saying, I think, is that there is a selectivity to people's liberal red lines that is sometimes galling and, on the face of it, hypocritical.
A great example of this was the progressive reaction to the murder of several black people in Louisiana by a disturbed young white man, Dylan Rooff I think he was called. Within hours the guardian had produced several articles calling this an act of White supremacy and indicative of institutional racism. It might or it might not, but when an Islamist atrocity is committed we are told not to jump to conclusions, that this is not Islam, to beware of the backlash etc.
Now I'm on the left, or at least until ISIS came along I was. So think how your average joe views this. They see a metropolitan left who are more interested in protecting the rights of international groups or cultures than their own. And if you don't think that was a factor in Brexit then think again.
It seems to me that the new left almost gets excited by stuff like the Burkini ban, reprehensible though it is. It's another opportunity to stick it to the man, to have a go at the west, all the while ignoring what Islamic conservative dress really represents, which is the suppression of rights that those same liberals would shout from the rooftops before you could say 'evil white patriarchy'.