How are your friends doing this?
” People I know who became US citizens had to turn over their other passports.”
****
bullsh*t
You mean a US citizen who is also a dual citizen of Canada is supposed to turn over the Canadian passport? Really...(eyes looking up)
Did you really just say that?? LOL
When you become naturalized, you must take an oath that you swear off allegiance to any other state/sovereign, but this is a manner of personal morals. It is quite legal and acceptable to maintain other citizenships for convenience.
Another case is that of people who are born holding two citizenships, who can use both passports throughout their lives.
I am certain about these rules. My wife and three children hold both United States and Russian Federation passports. My youngest (twins) obtained their US passports at the US embassy in Moscow, after the presentation of proof that they were born US citizens (my wife and my US passports).
If you know people who had to surrender their other passports upon naturalization as a USC, this was because their original country of original citizenship does not permit dual citizenship. Germany and India are two examples that immediately come to mind, as I know people from each of these countries who had to deal with this situation.
“People I know who became US citizens had to turn over their other passports.”
I am pretty sure that is not the case.