This is related to the country being founded by religious sectarians who themselves suffered enormous prejudice from the established churches and governing elites and were intent on creating a safe haven for dissenters of all stripes. Among most Protestant sects the emphasis on Biblical veracity and scholorship (both books) entirely alters the status of the Jews compared to pre-Reformation Church dogma. They also thrived in Protestant Holland and were welcomed back into Britain by Cromwell after the English Civil War. In the last century the Roman Catholic Church and other "established" Christian churches have also shed much if not all of their institutional antisemitism.
The broad statement that the Jews suffered under "Christianity" is the kind of half truth which Leftist Jews, many of whom are themselves Jewish in name and bloodline only, use to demonize all believing Christians of any type. It reeks of a divisive and deceptive political agenda on the part of the writer.
Excellent post! People raised in Judaeophilic American-style Biblicist chrstianity simply do not understand the rabid anti-Semitism of pre-Reformation chrstianity. It is a totally alien world.