Current American anti-Muslim bias is being commonly compared to 19th century anti-Catholicism. I think that's sloppy history.
Hateful behavior against belief in general is inexcusable in a society that espouses free speech and religious liberty wherever it happens. And it has happened in every time, whether against free-thinkers, Mormons, Catholics or Jehovah's Witnesses.
While violence against innocent newcomers and non-conformists is always wrong, the fears that underlie those hostilities are often distinctive.
Was the fear of Catholicism itself in the 19th and 20th centuries irrational, based purely on a blind defense of Protestant theology and democratic values?
Surely it was in part. Since the Reformation, Rome had been the symbol of the anti-Christ in many Protestant circles as well as a threat to a young nation whose ethos was democratic and Protestant.
But as the Notre Dame historians point out in their piece in the latest New York Review of Books, those fears were also grounded in concrete foundation. Popes in the latter half of the 19th century railed against egalitarianism and democracy in a frenzied reaction to Europe's revolutionary forces.