Surely Schlesinger would agree that those with strong religious beliefs are an integral part of the very foundation of American society and that their positive impact is extraordinarily great compared with the isolated destructive incidents of a few mentally unstable individuals. Those who attempt to play God, those who feel justified in taking innocent life, are scary. But the whole point of religiousness is to admit a limited viewpoint, a confession of creatureliness. To promulgate a misundertanding of committed religious people, as Schlesinger has done, is disappointing for a scholar of his reputation. A Jewish or Christian murderer just isn't living his faith.
Religious terrorists use religion selectively and dishonestly, ignoring such religious absolutes.
Resultant violence no more condemns religious absolutes than spouse abuse condemns marriage. To pretend that they do is to commit one of the worst idolatries of an era full of them. Also, for the record, most Christians are politically docile, and believers didn't start the culture war. Many secularists undeniably wish that American public policy was informed by the philosophy of the marquis de Sade. While living in society obligates one to respect others' rights, one is not obligated to cooperate with grave evil, much less finance it.