Ok, first of all apologies for the delay in getting back on this. That's entirely my fault to be honest, I've only just managed to read the threads in question, though they've been well flagged to me, as been away and lots of things occurring since I've got back.
I agree that the original thread should have been deleted for being deliberately inflammatory and I'm glad we got there in the end.
The reason for the moderating confusion in this case is that we don't have a knee-jerk deletion policy because a user or a number of users find something offensive. There are plenty of times when one person's humour, for instance, is another person's soft spot and we generally take the view that it would become very hard to know where to draw the line - who are we to decide that one person's hurt is more valid than another's? We'd end up routinely deleting everything on offence-caused grounds which would mean deleting an awful lot. On balance we'd rather go for free speech, debate etc.
BUT, as said, in this case that was the the wrong call. The subject matter is clearly serious, the hurt is profound and the OP's general subsequent posts did indicate that this was a thread that was started to inflame.
Secondly, I want to be clear that we absolutely don't want racist views on Mumsnet. I agree with everyone who's pointed out that racism can take the form of prejudice based on nationality and that we ought not to be too worried about the semantics of what constitutes racism or not, we ought to delete nasty, bigoted prejudice-based comment straight away. And to be fair, I think, we generally do.
So, all in all, we didn't handle this as well as we'd have liked. It can be incredibly hard sometimes to see the wood for the trees, particularly when there are lots of reports going down and people are angry. And some of these calls, as you know, are tricky to make.
Thanks to all for your input and apologies to those who've been upset by this issue.