What country offers greater opportunities than the US? I could agree with you if you're coming from most countries to the US. I don't agree when you say people will leave the US to go to some other country where there is little to no opportunity. What country do you imagine people will trade their US Citizenship to move to for opportunity?
Plenty of people move from France, Japan, Norway, to the US. I don't know where you get the idea that immigrants don't come from these places. I admit it's less common but it does happen.
I get this idea straight from the White House and the mouth of the POTUS. :) Which country greater opportunities than the US? - EU. I have one passport but I have full rights in 30+ countries. From the bad side it is softer.: no capital punishment, totally outlawed, no such dragonian criminal law - no 'jackpot' of convictions where for several petty crimes to be locked for dozens of years, no such merciless taxation system, no such social/wealth contrasts ... - enormous variety of culture, cuisine, education, lifestyles ... not so as 30+ countries but rather like 100+ worlds. That's why I strongly recommend USA to go back home and to join EU. Thus it won't even be necessary you to sell your citizenship to have full access here. The wealth comes from the good networking. Double the nodes and cut in half the connection costs and you have 16-fold increase in wealth.