I don't know if you're missing something, I just disagree. Really, this land has hundreds of "native" languages. Dine (Navajo) and Cherokee are two of the most widely spoken. English is an uninvited import.
Beyond that, there is one surefire way to boost a child's intelligence -- teach that child more than one language. Why would Americans specifically want less intelligent children???
And while it's wonderful and commendable that you plan to visit South America, many (most) Americans don't have that luxury. I think it's wonderful that we have enough multiculturalism in our own country of immigrants that even kids who can't afford to travel can brush shoulders with people of different backgrounds.
Finally, I would encourage you to reconsider some of your assumptions. I have a good friend who is a legal immigrant. She came here on a professional visa, has a green card, etc. This friend is a fully fluent English speaker. She uses both Spanish and English in her professional life, but she speaks Spanish at home because she wants her children to have the benefit of growing up bilingual. I also have two friends (married to each other) who were born in the US as the children of Mexican immigrants. Their daughter is a 3rd-generation American, but they speak Spanish exclusively at home, again for the benefit of bilinguality. Finally, my BIL and SIL, who have no Latino/a heritage and are culturally very "white bread" are sending their daughter to a Spanish immersion preschool for the same reason. So, I would urge you to reconsider the assumption that if you hear the Spanish language, it's because the speaker can't or won't speak English.
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ETA: Sorry, I can't help but add this. Patty K., if you are so attached to the English language, I would kindly encourage you to uphold the English conventions of punctuation and to consider proofreading your post. You aren't doing the language, or your political position, any favors the way your post now appears.