I do wonder whether the disconnect on not realising how much most immigrants cost us all comes from people not realising that they themselves are also being subsidised by other tax payers - so they underestimate how much each person in the UK costs.
In order to be cost-neutral over their lifetime, an individual has to average £40k income over their working life. Any less than that, and other taxpayers are subsidising them. Only 20% of taxpayers are actually covering their own costs. Yep, we are a strongly socialist country, with huge amounts of redistribution, whatever line Lefties spin.
In addition, we all enjoy the benefit of infrastructure which was built by previous generations: houses, hospitals, schools, railways, roads. Those cost much less to maintain that the original building cost. So we get the benefit of them in return for far less of the 'value' we ourselves produce. As the population grows, we get a smaller share of that 'free' benefit (eg roads or hospitals become overcrowded, so more must be built. HS2 was more about capacity than speed).
Obviously some immigrants are covering their own costs. Absolutely no one objects to doctors, engineers, medical researchers etc coming here, of any nationality or race. In addition to their genuinely useful skills (from an education the UK didn't pay for) and sufficient tax-paying, that type of immigrant usually integrates well. They bring a spouse (who may well work - since highly educated people tend to marry the same) and children who will almost certainly go on to professional jobs themselves once they finish their UK education (given their highly intelligent, education-focused parents) The children will hopefully have put down enough roots to stay in the UK and be highly-contributing adult citizens (including paying back their own UK education in UK taxes). Huge win for the UK.
But a delivery driver (maybe came on a care visa, but did 6 months of caring work if that, since delivery driving is more lucrative) who brings a wife and 3 children, plus 2 adult children and their wives and kids. Wives don't speak English or ever work outside the home. Even if their kids follow UK averages, only 1 in 5 of them will pay enough tax to support themselves financially over their lifetimes. We really can't afford hundreds of thousands of those. Each one impoverishes us all.
It's mind-blowingly disingenuous to pretend that all immigrants are the same. Conflating those different types of immigrants makes any statistic a nonsense, and is deliberately misleading.
Why do you think people do that? What is their agenda?
What we need is intellectual honesty and a fundamental change to our immigration rules so that every single immigrant is a positive addition to the UK. That's really not unachievable - other countries do it. And it's definitely not racist.