Why isn't immigration a valid solution to population decline? This seems like a classic paean to the old white country to me.
Immigration in Latin America is actually not very restrictive. Organized crime (from anywhere in the world) can come and go as it pleases in the region. Whatever you may have read on right-wing media, illegal immigration is rampant in Latin America.
The irony of some Americans complaining about Latinos now is rich. You didn't care much about them when the US govt was promoting dictators and doing everything it could to undermine the democratic will in the region (predominantly left wing in response to the incredible levels of legacy inequality) and why would you? It made many of your companies super rich which in turn provided you with nice, cushy jobs managing your "banana republic" natural resources. The local population though was saddled with no voice and (usually) murderous psychopaths as their "leaders". As a result they migrated in droves to the US, the richest nation on earth that also happened to be the closest. And now you complain. It would be funny if it wasn't racist too.