If you're involved in / on the opposing side of the religious rivalry, I imagine, yeah. But they'd say the same for the other side as well, I imagine. I get that's how bitter rivalries work - with both sides viewing the others as 'weirdos', to quote the poster.
If that's where it comes from, fine. Still seems strange for a Man United fan to feel that level of rivalry at them to an almost same level as our bitter rivalries. But I guess there's some that are also involved in that rivalry as well for religious reasons.
Actually, with this ostensibly being a Man United fan site, I often forget the Irish / catholic bias it has as well. So I guess the post makes sense, and will be well received, from that perspective.