What I fail to understand, if I understood correctly, at least that is the info we got here, is that person who did that was born and raised in UK? I mean it is, IMHO, so insulting to the complete community that has embraced you as one of it's own, although, let's face it and call it what it is, you don't belong there. This was never (This being Europe in general, west side of river Drina) in any way a Muslim part of the world. By this I don't think any less of Muslim religion (after all it is just practicing more or less very similar things in different way which has its roots in the mostly desert territory where it appeared first). So, if someone wants to live here where we live, it should go on without saying he/she should adapt to our ways and be thankful he /she is treated the same way as we are (which, sadly, can not be said in vice versa situations; try celebrating Christmas in Saudi Arabia, for instance).
So, IMHO act like this is deeply insulting to all the people who interacted with that person during his growing up and living in UK, wherever it was. It is, for me, even worse than, however horrible it was, that explosion he set off.
I just can't understand it, that is all.
My thoughts are with families of the victims who just went to a concert only to never come back again...