You want me to explain the argument against cheap labour to you? TL;DR it's not beneficial to those of low incomes.
You say you work in the NHS; can you tell me what is one of the most stress inducing and physically impactful type of job that affects people? Shift work. What are the effects of doing shift work? Increased risk of certain cancers, heart disease, ulcers, gastrointestinal problems, obesity, insufficient sleeping patterns, mental health issues, depression, anxiety, increased risk of strokes, to name but a few. Which jobs are most likely to offer shift work employment? Retail/Service industry.
An "easy job" like retail and it's health risks is often forgotten about except when people rage that a store is closed on a particular day. Then suddenly it's importance to them is made clear. Maybe there wouldn't be a need for more NHS staff if people were kept healthier, not having to work from 7-3am one day and then 9-6pm another, being paid properly or worrying about the next set of bills. But hey, if it's so awful, just quit and find a better job right? Well if everyone in retail/service had that attitude, people had best be prepared to say goodbye to many lifestyle institutions they often take for granted. It's not just your attitude towards migrants, it's your attitude that you think people won't do the jobs required in this country. They will, but we refuse to be exploited and as so long as the EU supports a system that exploits workers, that exploitation will continue. We want it to stop.