If citizenship isnt a line between two classes of people to which states owe obligations, then why isnt the USA obligated to pay for the healthcare of everyone in the world?
Why does medicare/medicaid end at the US border?
Empirical observation of the behavior of democratic demonstrates your position is not widely held.
Because we don't live in a perfect world... yet. But we should always be working towards more prosperity for all, greater access to resources/services, more sharing of knowledge/assets, and improving the lives of all people on the planet (not just our preferred groups/tribes). Don't you think?