Trust me man, although everyone says the old Catholic Versus Protestant thing, it really isn't like that. Religion has nothing to do with it these days, it's all politics.
The words of the song are 'up to our knees in fenian blood' (btw, that song in full pelt is unbeatable anywhere in the world)
A fenian is not a catholic, a fenian is a supporter or an affiliate of the IRA, so, quite rightfully, we sing songs of killing terrorists
.
They sing songs of killing soldiers.
Anyways man, Rangers is a club open to all. Protestant, Catholic, Islamic, Buddhist, Black, White, Atheist, Chinese or whatever, the club had its troubles in the past but we are now a very modern club and are very anti-discrimination.