Presumably the form for applying for benefits has a reasonably high bar for identifying the fact that you are in fact legally present in the country? Or how else do you imagine people living at "taxpayer's expense"? Just begging on the streets?
Do you know how much money the immigrants pay as taxes, health surcharge and National Insurance contributions in exchange for the right to live and work in the UK? Don't forget that the taxes, health surcharge and NI contributions of the immigrations are literally funding the NHS! I think it is fair to expect the contributors to get treatment when they are contributing so much to it.
In my experience, immigrants have low paying jobs and regularly use cash to avoid paying taxes. Most have no sense whatsoever of cohesion with the country they live in and instead make groups of similar culture that don't really try to fit in.
Yes, but generally a Medical Incident isn't really particularly desirable. You don't really get anything out of it other than "being healthy", which could be argued as being a right, and often a prerequisite for starting to contribute. Gatekeeping that just ensures they never will.