According to the New York Times (link to Feb 18 article here), despite a lengthy telephone call from President Obama to President Abbas, the Palestinian Authority took a hard line on the resolution and forced a vote, at the same time effectively forcing the United States to veto the measure.
American ambassador Susan E. Rice is quoted in the article as saying the draft resolution risked "hardening the position of both sides." And while she pointed out that the veto should not be misconstrued as United States support of continued settlement acivity, she also observed that the Security Council is not the proper place to try and stop such activity. "The issue should be resolved through peace negotiations, she said, and not mandated by a binding resolution," the Times article goes on.
It seems that J Street disagrees with such a position, and prefers that Israel be publicly castigated.
Odd behavior, for a "pro-Israel" organization, no?