Do you have any evidence to back any of that up? Personally I'm seeing a lot of mass migration across the world--not all of it wanted by the citizens of the countries being migrated to--right now, even without globally open borders. Why would having globally open borders do anything but increase this rate?
It's also interesting that you think globally open borders would only affect the culture of America, but you're okay with that, presumably because whatever Americans consider to be their culture currently is meaningless in your eyes compared to the glorious no-nations-no-borders future world you envision, which conveniently has no negative consequences and is only a positive thing for everyone (except Americans who like their country and culture more or less the way it is now but eh tough luck for them I guess)
It's also interesting that you think globally open borders would only affect the culture of America, but you're okay with that, presumably because whatever Americans consider to be their culture currently is meaningless in your eyes compared to the glorious no-nations-no-borders future world you envision, which conveniently has no negative consequences and is only a positive thing for everyone (except Americans who like their country and culture more or less the way it is now but eh tough luck for them I guess)