Why do so many citizens think that legal non citizens neither pay nor collect SS and medicare?

Because they are unaware of the laws - and if they are natural born Americans they have no reason to become aware of those laws. Most people are unaware of many laws which don't apply to them - nothing inherently wrong with that. It's hard enough to keep up with what we need to know; why should you expect people to keep up with laws which don't impact them?

Only illegal aliens cannot receive social security benefits, SSI benefits or Medicare EVEN if they pay into the social security system and pay income taxes as so many illegal aliens do.

Source: I was a social security claims rep for 32 yrs.

Dues to the law any non senior citizen cannot get SS or Medicare because they did not pay into the system..

But when a non senior citizen becomes a US citizen they can get the SS benefits but not Medicare, they can get Medicaid instead.

Logic says: If you are undocumented AKA; illegal and work in the United State with a legitimate company, taxes are generally paid by your employer. Key word "Illegal" probably means you are paying taxes on a fake SS number so you are either talking about fraud or ignorant government. That said, that's why!

Because many oldsters enjoy watching Fox news so they have a limited view.

If you are legal, then you have to do like the rest of us. You are being mistaken for an illegal.

Because they do.