Had a quick look back and it appears to be mostly the 'outers' accusing the 'inners' of being racist, especially left wing 'inners' but hey ho, maybe you see something I cant
As for uncontrolled mass immigration suppose the best argument is that the most successful countries in human history have been the ones with the most immigrants, and the insular countries have usually been poor relations/basket cases
Not sure if its chicken and egg, success leads to immigrants rather than immigrants lead to success, probably a bit of both, either way you should be pretty happy about being lucky enough to have been born in such a place that people will risk death trying to get to
The real reasons for mass immigration are.
U.K. Economic growth in working age population and net contributing population comes mainly from inflation and immigration factors so to maintain growth, tax revenues, protect government spending and attack deficit mass immigration has been required .
This protects the UK also from the demographic time bomb, immigrants on average are early in their career so have tax paying wealth creating potential and that is used to fund the ageing UK population for health and retirement.
The FT had a great analysis from 1995 to 2011 showing Eu immigration added a net contribution of 8.8bn to UK coffers for example. The drain on the UK coffers from native Britains in that time was 604bn (obviously not like for like as one population was exponentially bigger than the other)
It was also demonstrated that those industries with a higher % of immigrant workers had higher productivity concluding each X 1% rise in immigration brought an incremental 0.07% productivity improvement .
Other arguments around diversity, skill based, demand, labour flexibility, lowering the age of population, specialist requirements in certain sectors etc can also be made.
There is also the reality that digital, globalisation and technology Have made competition , capitalism etc truly global and anyone who truly believes in capitalism and globalisation actually should support the free movement of capital and labour and therefore immigration for economic reasons. It is somewhat ironic that it is really the left that should oppose immigration and the right who should be supporting capitalism if true to principles
With digitisation , the taxation issues around transfer pricing , global freeing up of capital etc the March of history is towards greater movement of people and capital, bigger trading blocks , global rules etc and that is a tide that cannot be stopped.