There's an issue here though, it's not just the fact some Rangers fans are protestant or orangemen is it? Personally, I couldn't give a f**k what religion or political viewpoint someone has when they turn up to a football match. It is Rangers fans that impose it upon me when I encounter them.
I attended the cup game at Pittodrie a few weeks ago and I was serenaded about Bobby Sands, the UVF and god save the queen before the game had even started.
You might say that's not representative of the Rangers support but it's consistent with any experience I've had of them at Pittodrie, Ibrox or Hampden. So it's not just that they are Orangemen, but that they aggressively want to let everyone know they are. Whether you like it or not their songs are aggressive to those who oppose that view. This is why it isn't just a case of abusing them because they are protestant or whatever.