Because they paid taxes while working here legally.
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That's their choice ---no one begged them to work here, if they don't like our taxes they should work at home. I pay taxes too but don't qualify for welfare programs. If you work past 65, you don't get a social security check even though you paid more taxes into it and continue paying into it. Giving welfare and food stamps to all that qualify in Mexico might sound nice but why stop at Mexico? Guatemalans, Hondurans, Brazilians, Peruvians and all the rest might also like these programs but like Mexico if they do they should make their own programs.