If you didn't read the Op-Ed, he's criticizing the National Popular Vote Compact, which will ensure the winner of the popular vote wins the presidential election when enough states ratify it. It's hard to understand Jacoby's argument because his point is (to translate) "you Democrats are so dumb, like I once was, then I became a conservative" with an imitation of Buckly-Hitchens flair.
But what I think he's saying is this: "Suppose the Democrat wins the popular vote, then MA will give it's electoral votes to them. But they almost certainly would have won the state. Now suppose the Republican wins the popular vote. There's a good chance that the Democrat won MA, so the outcome is to flip MA's 12 electoral votes in the Republican column." This is how the compact "nullifi[es] of [voter's] vote[s]."
That almost sounds like it makes sense. The compact, most likely, will make MA voters have less say in the election because it increases the chances that Republicans will win. Except that it doesn't.
What Jacoby forgot is that, while it's true that under the compact MA's electoral votes will never swing to a Democrat, it's possible votes in MA could swing Texas into the "D" column. In 2000, for instance, Gore's 787k margin of victory in MA also gave him a 545k margin of victory in the popular vote. If the compact were operative in Texas that would have flipped Texas' 34 electoral votes from Bush to Gore and Gore would have been president--thanks, of course, to MA Democrats. But under the compact, Jacoby assures us, MA Democrats would have nothing to gain.
(That only applies to a state's vote as a whole. The issue for a single voter is the probability that without their vote, under the compact, the popular vote is a tie or, under current law, neither candidate has 270 electoral votes without their state and the election in their state is a tie. For MA it's obvious the tiny, tiny probability of the former is many, many orders of magnitude larger.)