Unilateral disarmament

I've blogger about this before, but now I see from Politics NJ that Democrats in my own state are pushing a bill to force our presidential electors to vote for whoever wins the national plurality regardless of the vote in New Jersey.

The Senate State Government Committee will consider legislation that would require New Jersey's electoral votes to be cast for the candidate who wins the national popular vote, not necessarily the statewide count in New Jersey. S-2695, sponsored by State Senators Richard Codey and Raymond Lesniak, seeks to include New Jersey in an “Agreement Among the States to Elect the President by National Popular Vote,” which would be effective only if enacted by enough states to "collectively possess the majority of the electoral votes required to decide a presidential win – currently 270 of the 538 electoral votes."

As I've said before, the only states that are seriously considering this tend to vote Democratic. So, why would the Democrats unilaterally disarm when it can only hurt them? If every state agreed to this, I think I might go along, but when only the Democratic states agree to lose their electoral votes if a Republican wins the national total, that makes no sense at all.