Imagine if the DPJ candidate had won. After all, they did join hands with the Communist Party and embrace the get-the-US-troops-out-of-Okinawa candidate.
The DPJ-JCP GTUSTOOO demands are unlikely to be met in the forseeable future in any case. The national government would not agree to kick US troops out of Okinawa and perforce Japan. (Besides, the people of Okinawa themselves will have second thoughts if such a thing ever looked likely; the national government will be loathe to compensate Okinawa for the loss of economic and fiscal benefits currently flowing as the result of and in compensation for the US presence.)
But does that mean that the DPJ would have a free pass on national security, catering at no cost to popular sentiment, while the LDP suffered the brunt of US and local frustration? In fact, by way of their commitment to GTUSTOOO, the national DPJ would be seriously constrained in any national security debate. And any real influence they are able to exercise would in the long run have negative ramifications throughout the Japan-US security relationship and ultimately undermine it altogether.
The DPJ remains a grab bag of a wide variety of elements, ranging from the moderate wing of the old Socialist Party to youthful nationalists more in tune ideologically with their LDP counterparts. Nevertheless, in recent years, seeking to differentiate themselves from the LDP, they may have had no alternative but to position themselves to the left of Junichiro Koizumi and now Shinzo Abe. An absurdity like total agricultural self-sufficiency as an electoral campaign platform could be understood in this light as a throwaway line, and not to be taken seriously. But GTUSTOOO would have real-world consequences. It directly affects our security and diplomatic relationships with our major ally.
Perhaps it is just as well for the DPJ that it did not have to cross that bridge just yet, while they continue their struggle to figure out who they are.