Heck, it's a struggle to convince many of them that Catholics are Christian at all, and "the Pope is the antichrist" used to be a normal, mainstream comment in American newspapers.
It is somewhat a piece of irony that the Pope generally holds a more favorable reputation in the minds of the irreligious in America than the religious. Even the average Catholic likely does not have as much respect for the Pope as some of the commenters here.
In America, anti-Catholic sentiment was extremely strong until relatively recently, and then only because religiosity (and thus the reason for it) has declined. All the theological division still exists, it’s just less striking in a world that’s much more irreligious and in countries where vastly different religions (Muslim or Hindu) are present now in real numbers.
Practically all the pro-Pope sentiment I’ve seen in my lifetime has been from various flavors of atheists, agnostics, and other areligious types. Catholics themselves generally hold more respect for the office than the person, and Protestants are almost uniformly negative on both.