I've spoken about this on other topics. I think this subject is deeper than what it actually is in the eyes of the fanatics who spout this rubbish. let me explain my theory.
There is a new "left wing" movement that has been gathering pace over the last couple of decades, not just in the UK, particularly strong in America. In fact it's not left wing at all, it's right wing. Anyway these groups have slowly politicised groups and rely heavily on them being "victims". Women, Jew, Asian, gay etc. Have all been made into political pawns, to the point where if you believe in the wrong politics you are somehow the wrong type of Women, Jews, Asian, gay etc. Their biggest offence when they lose logical debate is illiberal insults. You agree with me or I will call you a xenophobic, racist, homophobic, misogynistic etc. Evidence is clear from many sources from the forum to the mainstream media.
Now this links with brexit because brexit has been their kryptonite, I use that because they have been a Superman like force in politics up to Brexit. The very next day after the referendum Dianne Abbott, Caroline Lucas and co was out shouting their "safe place" card, the trump card that makes everything go away, fat turns to meat, straw turns to grass with a shout of "Racism". But brexit has not gone away, this is the problem for them.
So I believe they know the difference between immigration control and reduction or stopping of immigration full stop but can't say that now, because in doing so would risk their "safe place" card forever. They need brexit stopped and the "safe place" card back in place.