a) The Court not only follows the tide. It pulls the tide. The Court's decisions affect social movements--obviously, or social movements wouldn't always be trying to fight their battles in the courts!--and can add prestige and respectability to one side or another. The Court helps create the tide, and shouldn't present itself as a passive bit of flotsam.Simple, elegant, and considerably smarter than anything Balkin has written that I've read.
b) Those social movements turn to the courts often because they have failed to win enough, or fast enough, victories in the legislature. That in itself seems to show that the tide has not necessarily turned, and that the movement's future is still uncertain.
c) Tides turn back. Cf. welfare reform as vs. the welfare-rights movement (which appeared to be gaining steam throughout the 1970s); the unpredictable political effects of America's periodic religious revivals and "awakenings"; the surge of pro-life beliefs among young people. This can either be a Justice Janis impetus to "get it while you can"--make as many controversial rulings as you can get away with before the tide turns against you--or as a call to a degree of humility about one's own ability to predict the effects of technological development, political pressure, and a country of restless souls.
and d) If these practical concerns (you can't always tell what History will say) are the only barriers to C-judging, the Court really is just a philosophical tribunal that refers to the Constitution as a kind of sacred hidden totem, useful for conferring legitimacy but not constraining upon Court decisions in any major way.
UPDATE: Eve's permalinks aren't working, so just go here and scroll down.