^The answer to that one is Saudi Arabia, where the government brings in enough oil revenue such that Saudi citizens need not be taxed. A few other countries here and there are similarly "free."
But, regarding the "slavery" question
Thirteenth Amendment wrote:
Section 1. Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Section 2. Congress shall have power to enforce this article by appropriate legislation.
"Do you think it is good to be a slave" is simply an absurd question. I'm grateful to President Lincoln for having put an end to slavery.
Every hour spent on earning a wage which is then taken by force is involuntary servitude.