“…an ageing population needs younger immigrants to pay their pensions. You'll be in trouble without them,”
This has been adequately covered in the other question that has been referred to. But, in short, it doesn’t. What is needed to pay State pensions is for the scheme to be run on commercial lines with the current contributions being invested for the future liabilities to be provided. As it is it is run like a Ponzi scheme. That’s why it needs a greater number of younger contributors to cover current payments. And, of course, not usually mentioned but quite important when debating this strategy is this: the young contributors that are shipped in (if indeed they do turn out to be contributors) will eventually get old. They will need pensions. The current contributions when they reach that age will be even more insufficient than now. So what do we do? Of course it’s bleeding obvious! Ship in some more young contributors! But hang on though. They will eventually get old. No problem…ship in some more young contributors (continued until the UK sinks under the weight of humanity on its shores). Utterly preposterous to anybody prepared to look beyond the middle of next week.
“You don't see the benefits that will flow from a culturally diverse society, then, Bazil?”
If Baz doesn’t I most certainly don’t. My imagination does not stretch anywhere near enough. In many areas of the UK there is no cultural diversity at all. Vast areas have become zones of single ethnicity populated entirely by migrants and their descendants. The promised benefits are simply not significant enough because many of the incomers simply refuse to integrate with those who were already here. Of course we can all go for a Ruby on Saturday night, but that's about it.