The OP's statement doesn't seem false. Argentina is simply giving these people permission, even though their standards are apparently quite lax.
That is the method to obtain citizenship for most without means is you must act without permission and then run down the clock.
The US immigration authorities do occasionally do raids on employers that are known to employ lots of illegal immigrants (which can be people who simply walked over the border, or people who overstayed a visa). It's not unenforced. For people in higher socioeconomic strata that blend into the population better, it's not that well enforced probably because it's just hard to find them, and local law enforcement doesn't deal with it.