It's all politics, the majority party tries to pass legislations, the minority party tries everything to block them. If the majority party passes legislations, they can say to their voters that they got things done. If the minority party successfully blocks legislations, they can say the majority party was too partisan and wasn't willing to compromise. Doesn't matter if it's Democrat or Republican.

Right now Republican is still a minority party because Obama is president and Democrats still control the Senate. Therefore Reid will try to pass immigration-related legislations like the Dream Act, and the Republicans will try everything they can to stop it.