I'm saying it full stop, the only people who want the UK to age to death for the sake of keeping out immigrants are racist, I said it and I meant it
Q.E.D...
Let's see what he considers concerns and how he can evidence their existence in the UK specifically.
Let me take a step back here. I believe it is ultimately possible to have too much of anything. As a rough analogy, drinking eating and physical activity are all necessary to stay alive... but these activities will also become harmful, even fatal, when done in excess: drinking six liters of water in three hours can kill you.
Similarly, a degree of immigration is clearly beneficial, but there are associated costs as well, both direct and indirect. At some point the costs (at least for a generation) likely start to outweigh the benefits. I have no idea whether the UK has a long way till that point or is already past it.
This would by no means be a simple calculation - the costs and benefits would affect different social groups and localities unevenly and would come into play at different times, insofar as they would be objectively quantifiable at all.
As a random example... suppose a community where violent crime was previously non-existent receives 1,000 immigrants, just 1% of whom form a gang and get into habit of robbing phones from kids at knifepoint (something which might not have occurred had there been just 100 of them) ... how do you price that cost vs the benefits the group brings? Just the cost of dozen cheap smartphones? Or also the time, stress and fear of 1,000 local mothers who are now too worried to let their kids commute to school on their own and start driving them there instead? Costs associated with catching, prosecuting, re-socializing/rehabilitating the offenders (which might be taken on...or not)?
Before a society can even get to productive discussion about this, two things are needed imho - honest acknowledgement that there are immigration has also negative effects and costs associated with it - and as much as unbiased statistics about these as possible. A lot of European countries don't seem to do well in either regard, UK included. I don't have evidence you're asking for, only anecdotes and no easy way to separate disinfo from truth.
Things are further complicated by more unfortunate life facts, namely:
- that some people totally are racist;
- that being racist does not automatically invalidate all concerns they may have;
- that existing framework of international treaties, while being A Good Thing in general (we should NOT be returning to the world described in Remarque's Flotsam and Arc de Triomphe, with stateless and/or refugees being ping-ponged across state borders with no way out) are quite easily exploited by criminals, which breeds additional resentment.