That's exactly what I was thinking. Sociopaths get off on your pain, addicts get off on your money. If an addict could steal your money and make you feel like you're walking on sunshine, they would. Well the inverse is true for a sociopath, if they could make you rich but miserable he would. Addicts may do wicked and evil shit, but usually they still feel remorse. It's just the compulsion to use is so over powering. It is extremely hard to overcome an addiction, especially by yourself with little to no support and no tools.
It's a shame you feel that way. There's no rehabilitation in prison. So saying that's the best place for him is saying he is a lost cause, and that's sad to me. In my opinion, people only become lost causes when everyone turns their back on them.
Actually quite the opposite, again sounds like an addict not a sociopath. I'm pretty sure sociopaths usually tend to achieve some moderate form of success even with their anti-social behavior. Their willingness to lie, cheat, and steal to get to their top often does get them ahead.
So it sounds to me like you have an addict on your hands. He probably has a several hundred dollar a day habit. And he probably feels totally trapped in his addiction. You didn't necessary do the wrong thing kicking him out, because enabling an addict does not help the situation and providing free living is enabling. Nor can you blame yourself for someone else's addiction, plenty of people with perfect childhoods turn to hard drugs, people from all socio-economic classes, intelligence, age etc.
But if you totally turn your back on your son, and are not there to support him, then you failed your son. If he ever does decide to clean up his act and go to rehab, he will need support. Getting clean can be incredibly scary for some people, and it's hard to do by yourself. Every aspect of ones life needs to be changed, from friends & acquaintance, to daily activities. Without a loving and supporting family backing you, it is very easy to lose sight of that light at the end of the tunnel and slip back into active addiction.
Just remember, there's a big difference between tough love and no love.