That's Will Wilkinson's advice to "bad voters":

When enough people vote badly–from ignorance or bias, for example–the result is often bad policy. The quality of policy matters to the public good. Higher-quality democratic decisions, and better policy, can be secured if bad voters choose to abstain.

By that Will means people who tend to vote Democrat:

There are more Americans inclined to vote Democrat than Republican. But the poorer and younger Democratic-leaning voters are also least likely to show up at the polls. Therefore, promoting the idea that it is a civic/moral imperative to vote disproportionately benefits the Democratic party by getting higher levels of participation from the poorer and younger voters, at whom much of the marketing blitz is focused. And, of course, the American media establishment overwhelmingly favors the Democratic Party.  However, higher levels of voting from these groups pretty much ensures greater electoral pollution. Were most Americans Republican-leaning instead of Democratic-leaning, but the media was exactly the same, I predict we’d see an outpouring of sympathy for positions like Brennan’s from intellectuals and media elites.