Immigrants harm an economy badly.
I've seen you mention before you have started studying Economics, but you make this long sweeping rambling post without any citations or actual analysis. I'm sure you understand, as a fellow student of Economics, that this does not justify your thesis (quoted above). I'd like to focus on a few parts, although there are many, where I believe you are mistaken or failing to comprehend the entire picture.
Then you bring in an immigrant. Who works all week and then sends two thirds of his money back to his family in his homeland. That wealth is then spent into the immigrants economy. It is lost to England. Its gone. Now once you have several million people queuing at Weston Union to send £billions around the world every year, you can see the devastating effect it has on an economy. Great for the parasitic country providing the immigrants. Utterly destructive for the host nation.
Western Union, being only one company that handles money transfers, generated
$5.6 Billion in Revenue in 2014. If immigrants are using your nation's financial services, and hence generating revenue for the nation, there is a non-negligible amount of economic activity happening. You are also ignoring the addition to a workforce that immigrants can bring. This can be both in the form of cheap labor (See:American Agriculture) or in the form of experts on niche topics (See: High-tech and Academia jobs).
You'll hear a lot of left-wing twaddle about how much immigrants contribute and how its a net positive figure. What that figure doesn't account for is the outflow of wealth and the huge infrastructure burden associated with the huge influx of people. The extra hospitals they need, places of worship, the public amenities, more roads, more schools, police, fire crews etc etc. All of that has to be found. When you bring these figures in, you can see why nations like Britain now say they can't afford services like the NHS and police and have to cut them back.
This sounds like a lot of economic activity, and legal immigrants are paying taxes to help fund the public portions of it. Sounds like a good thing to me, if we're looking at it only at face value. I don't really have the time or interest to do a full literature review and analysis over this issue.