The article is more nuanced than the headline. If you're just reading headlines, though (because you're skimming a news aggregator, say), then you get the idea that people think she can't be a Supreme Court justice because she's Catholic. Down in the article, you find that people think that she can't be a Supreme Court justice because they think it's problematic the kind of Catholic that she is. (Or at least because of the political implications of the kind of Catholic she is.)

That's coming from people in office, not just from random crazies on Twitter.