What principle?
That we should not seek an agreement that will ever so slightly reduce the threat of nuclear destruction? We should not seek the warming of relations with Russia that this will bring? We should not seek the high ground we will obtain in dealing with nuclear non proliferation issues? We should not seek the benefits this will bring us in costs maintaining obsolete Cold War era military postures? We should not gain the the support this will bring us in restraining Iran?
Reagan signed nuclear agreements with the Soviets. There are no principles here to fight against this agreement.