I'll join Kevin in being flummoxed by the idea that liberalism "stand[s] for imposing public policies on democratic majorities that don't want them." Jonah seems to mistake the pursuit and eventual rejection of unpopular programs as some sort of philosophical tenet. He mentions "bussing, racial quotas, gay marriage, Title IX, etc" as evidence of this tendency, but that technique would appear to implicate conservatism too: "Social Security privatization, Medicare reductions, the abolition of the Department of Education, banning federal funding of embryonic stem cell research, continuing the Iraq War, the continual obstruction of universal health insurance, etc."
Political parties push a lot of ideas. The ones that everyone likes -- say, Medicare -- become consensus positions, the only remaining arguments questions of implementation. Those that folks dislike are dismantled, either by voting their supporters out of office or pressuring their backers into changing their minds. And some exist in a middle ground, currently unpopular but growing less so, or seeing more moderate alternatives (like civil unions) gain momentum. Indeed, part of the purpose of political parties -- not to mention defined terms for politicians and insulation for the Courts -- is to create the space to convince electorates that policies they don't initially like are actually beneficial. Sometimes the programs are defeated (busing). Sometimes they grow sacred (the Civil RIghts Act). So it goes.
It bespeaks a profound blindness that Jonah can only see evidence of unpopular priorities in liberalism. He should ask his magazine's founder how popular his ideology seemed at the outset, and whether that proved static.