What separates successful people from unsuccessful, in every discipline, is BELIEF and PERSISTENCE. Those that tell others they can't make a living treasure hunting are projecting their personal doubts and limitations. People have different levels of ambition and motivation. When people feed their doubts, they go about producing the "evidence" to support those doubts.
It takes the right circumstances to treasure hunt full time but every change in occupation requires planning and sacrifice to some degree. If you're working a full time job to support a family, you might be relegated to weekend hunting until your circumstances change. I know someone who started treasure hunting full time when his business closed due to the economy. A few years ago I read about a college graduate, while looking for work, started metal detecting. After some great finds and no luck finding work eventually became a full time treasure hunter. If anyone wants to go full time - go for it. Ignore the Nay-Sayers and failures and learn from those who are successful.