I hear you, Taffy.
I recognize it's hard for us in North America to make a judgment on the Manchester risks of the UK.
Personally, I was raised in a "diversity" environment, where we had to open our minds and hearts to people of all origins, mostly refugees. And it has worked quite well for us so far (not perfect, but quite well - I would risk a percentage of 98%). I understand it's not the case everywhere in the world: Diversity does not work well in the Middle East for example. And it is less accepted in the US since the trump election (there are more and more hate crimes).
Yourself, Taffy, with all your heart (I know you are a good father), you want Esther to become well integrated in the UK, accepted by her peers in school, and later on, by her peers at work.
So, where do you draw the line? Immigrants or citizens of foreign heritage are OK in the UK if they have at least one UK parent who will help them to integrate, but Muslims are not OK because they don't integrate (they don't integrate well in France or Belgium either; maybe also in Poland and other former USSR countries): Do I understand you well? The whole Brexit thing is about Muslims, right?

Not about people of African heritage right? Or are they included in the Brexit anger? (I am honestly asking the question, not trying to be ironic as for us in North America, it's not always clear).

So, historically, we are going back to the Ottoman empire trying to invade Europe. It lasted for centuries and centuries. Europe resisted. And it still does. What Brexiters say is close the borders: Do I understand well?

The UK brought a lot of people from Africa into the UK and into the Americas; these people did not invade, they did not want to come here. What do Brexiters say: These people should return to Africa?