I'm curious. How does or how can a person renounce citizenship in the U.S. and leave the country without that person having a passport from the U.S. Or from any other country? I'm not planning to do this. I'm just really curious to know because I've read about people renouncing their citizenship for different reasons. Most think it's because of taxes. I'm sure people have other reasons. Can someone tell me how or if it's possible for someone to renounce citizenship if they don't have a passport for the U.S. or any other country?
You could ask for political asylum in another country. Let's say you are a spy (or wish to become one). You visit the embassy of the country you wish to spy for and if they agree, they will give you papers to help you get out of the United States or arrange for a travel method that doesn't involve documents such as passports.
It used to be possible to travel to Canada, Mexico and the Bahamas without a passport but I do not know if post-9/11 this is still the case.
You could certainly get a sailboat and sail to Cuba and ask for asylum, but you probably wouldn't get it.
Once upon a time refugee travel documents were fairly common, but I don't think this is still the case. Cuban refugees were given travel documents by the United States that functioned as a passport but which were not passports. The Vatican issued travel documents after WWII as did the Red Cross. Jewish refugees from Nazi Germany went to Shanghai, China because it was one of the few cities in the world that would accept individuals without the need for visas.
I cannot rule out any loophole or freak occurrence but reasonable countries have rules in place to avoid such issues. People who renounce US citizenship for tax reasons (as opposed to ideological or personal reasons) will also secure another one beforehand because being stateless is extremely unpleasant and you need to live outside the US to be out of the reach of US taxes.
In the case of the US, renouncing citizenship is only possible from abroad. It seems that you don't have to prove you are a citizen or long-term resident where you are when renouncing your US citizenship so you could still find yourself staying somewhere illegally or become stateless with no easy way to travel but that wouldn't be the US' problem.
Because statelessness is generally considered to be a problem, other countries (e.g. France or Germany) have even more restrictive rules and only allow their nationals to renounce their citizenship if they already have or can be sure to get another one. Similarly, it's not possible to loose or be stripped of the French or German citizenship if you don't have another one. Both these countries and many others are also party to the 1961 Convention on the reduction of statelessness, which the US is not.