It's ironic, too, since the separation of church and state benefits Catholics. I don't know what delusion they're operating under, but if the government actually established a religion and enforced its rules, the US government would never pick Catholicism. They have as much to benefit from the separation of church and state as we do.

Wikipedia describes anti-Catholic sentiment in colonial Maryland, the supposedly Catholic colony:

The Colony of Maryland was founded by a charter granted in 1632 to George Calvert, secretary of state to Charles I, and his son Cecil, both recent converts to Roman Catholicism. Under their leadership many English Catholic gentry families settled in Maryland. However, the colonial government was officially neutral in religious affairs, granting toleration to all Christian groups and enjoining them to avoid actions which antagonized the others. On several occasions low-church dissenters led insurrections which temporarily overthrew the Calvert rule. In 1689, when William and Mary came to the English throne, they acceded to demands to revoke the original royal charter. In 1701 the Church of England was proclaimed, and in the course of the eighteenth century Maryland Catholics were first barred from public office, then disenfranchised, although not all of the laws passed against them (notably laws restricting property rights and imposing penalties for sending children to be educated in foreign Catholic institutions) were enforced, and some Catholics even continued to hold public office.

Discrimination against Catholic people because of their religion has deep roots in this country, and having a system where laws get made to support or keep down a certain religion isn't a system that's going to benefits Catholic Americans.

Furthermore, considering how often the "dual loyalty" charge has been leveled against Catholics (most famously against Kennedy, with people suggesting he'd take orders from the Pope instead of from the American people), you'd think a Catholic clergy member wouldn't want to be on the news for saying that the Church's teachings from the Vatican were motivating their participation in a political initiative. It assumes one of the worst stereotypes of Catholic people - that they put the values of the Church ahead of American values - and assumes they'll follow through with it because, well, they're Catholic and Catholics need a Pope to think for them.