Because
Not only is it the moral thing to do, it's also significantly cheaper than the tax payers covering the cost of their emergency bill which we already do.
Now that i answered yours, answer my question. do you think someone should die because they visited a country and don't have Healthcare?
because no country in the world provided free healthcare to anyone who just happens to be in the country.
1. Universal healthcare isn’t actually free.
—it is instead paid for through the tax payers.
2. Prevents medical tourism
—so let’s go ahead and counter the idea that everyone there is paying sufficiently into the system to receive exposure healthcare
— for example, if you go to the Canadian side of Niagara and you need a kidney Transplant you aren't going to be fully covered because you purchased a replica barrel and a beer
-- at some point your expenditures outweigh your resources
3. Capacity constraints :
-- there's a finite number of doctors, medical beds, medicine, and specialists
-- as such you have to address these issues when making a system
-- increased wait times and the inability to treat those paying for the system raises a different MORAL and ETHICAL counter argument.
4. You continue to provide the same life threatening and emergency care you still do
--that directly addresses the moral argument you introduced
TLDR;
THE PEOPLE WHO PAY I TO THE SYSTEM RECEIVE EVERYTHING AND THOSE WHO DO NOT ONLY RECEIVE EMERGENCY CARE