Conservative activists tend to lobby on behalf of a fairly comprehensive agenda, stretching from abortion to gay marriage to tax cuts to education spending. (Even conservative organizations set up to lobby on single issues, like business regulation or gay marriage, tend to coordinate pretty closely with other conservative activists....)But they all manage to come together as Democrats, don't they? So what's the difference between conservative activists and liberal activists, other than party affiliation? It's a fairly consistent set of principles -- generally present in conservatives and generally lacking in liberals.
Liberal activists, on the other hand, tend to be much more focused on single issues: the abortion rights people don't get too worked up about labor issues, labor doesn't get too worked up about environmental issues, environmentalists don't get too worked up about gay rights, etc.
Libertarians, on the other hand, are completely principled and hew rather closely to their principles. Perhaps that's why they'll never govern.