I am unaware of the endings for Vegas and Primm, I haven't done a CL walk through yet. However, to the comment about enslaving traders, there is a very simple answer. If CL raided every trader then NO traders would go to them. They would know they would get raided from stories and CL would eventually run out of supplies/need to go look for them by themselves.
Even if you were a citizen there would still be the Legionnaires who think they are better than all the other citizens. In high school you have the jocks who think they are better than everyone else, but imagine if your whole school was filled with them and there were only a handful of "regular" kids. Being picked on all the time would not be gratifying. If you wanted to get any respect from the Legion it would come down to simply joining them.
Not really sure where you are going with the currency thing. CL doesn't make everything out of thin air so they would need some form of money to purchase goods from traders. Clearly they don't pay for labor though.
Even if you were a citizen there would still be the Legionnaires who think they are better than all the other citizens. In high school you have the jocks who think they are better than everyone else, but imagine if your whole school was filled with them and there were only a handful of "regular" kids. Being picked on all the time would not be gratifying. If you wanted to get any respect from the Legion it would come down to simply joining them.
Not really sure where you are going with the currency thing. CL doesn't make everything out of thin air so they would need some form of money to purchase goods from traders. Clearly they don't pay for labor though.
The army does not make up the majority of the Legion's population. That would be impossible. People like Dale Burton far outnumber the Legion's military in their own territory. We only see nothing but Legionaries and one Dale Burton because the Legion presence in the Mojave is a military campaign.