Those who get elected are generally accountable to the American people (although gerrymandering and Citizens United has done away with a lot of that). Billionaires, on the other hand, are really only accountable to their shareholders.
I think most people have their own best interest at heart first, but that doesn't make them all cartoon villains plotting global domination. While many just want power and authority for themselves, there are also those who want power and authority to make a positive difference in the world. I think you have to look at each person's track record before dismissing them outright
