> I have yet to see anyone who floats this thought acknowledge that some cultures are in fact better than others.
That's... that's because most cultures aren't.
> they will degrade and destroy everything we've built with our nicer, more secure, more productive cultures.
There are many, many flaws with the culture of the USA you're conveniently ignoring here. I mean, if you use torture or capital punishment as a metric for how much better a country is, then America is extremely backwards compared to most (or even all) other places on Earth. You're not even a democracy anymore. You're still (on the whole) having problems with racism and sexism, something that has been largely sorted out in Europe (Even though we still have a way to go, we don't have as far a journey as you!). Hell, religious fundamentalists control a large part of your country still, and you're having to fight large parts of the country about the right for schools to teach scientific fact over religious fiction! You're having huge problems with surveillance, and the sheer extent to which your rights and freedoms have been curtailed by the state is still only just becoming apparent. You don't even have a universal healthcare system for crying out loud! What seems like every other day, there is a mass shooting happening in some place or another -- I can't really think of anywhere in Europe with such a rate of gun violence. And that's including the places where guns are not banned.
In what world is such a place 'nicer' or 'more secure'?
Additionally, do you think that it's beneficial and progressive to limit the fruits of modern science, knowledge, etc. to a subset of humanity?
Alternatively: So you think that some people are more deserving than others in the rights that they have, purely because of where they were born, and happen to live?