Liberals, why bother voting for Democrats instead of 3rd party or Republicans?

In the year Obama and the fool proof majority have been in office they have gotten absolutely nothing done. No card check, no UHC, no climate legislation, no end in sight to the wars, nothing. They promise to do this and that, and that's how they get elected, but once in office they do what they're told by their true employers, the lobbyists and special interests. So why bother voting for them? Wouldn't it be better to vote with your conscience (3rd party) or get the Republicans in office so they can hasten the demise of the country quicker? I like that option personally, all these silly lower cl cons that vote for Republicans would change their colors overnight when things get intolerably bad for them, just like the government was dearly afraid of happening in the 30s, or in the 1910s. The radical spirit of the 1910s or 30s would be good for us.