Democracy requires the continuing participation of the losers, and if you do not have the stones to play the game again the next time then you are part of the problem, not part of the solution. The sooner the passionate people get disappointed and leave the government up to those of us mature enough to recover from the agony of defeat, the closer we will be to substituting casual, fun-loving partisanship for the bitter, spitting version that has dominated in the last 15 or 20 years.
Put differently, Andrew Sullivan evidently thinks it is a problem if his passionate correspondent drops out of politics, and I think we would be better off if he did. I yearn for the days when we could talk about politics over beers with people of the other wing and walk away looking forward to the next such conversation. All these passionate, easily-disappointed, thin-skinned people take all the fun out of democracy, and make the country much harder to govern besides. Good riddance to 'em.
I always find post-election whiners, acting as if their candidate losing is the end of the world and calling for massive changes to the system or threatening to take their ball and go home (or move to Canada), a big turn-off and a sign that they're someone I probably won't be able to have a constructive conversation with the next time around. Part of the democratic process is not only having a winner, but also a loser, and if you're going to play the game you're also going to have to understand and accept that from time to time you'll be the latter.