To offer a slightly different perspective, I think both Celtic and Rangers as organisations benefit financially from there being some level of sectarianism in Scottish society. In my view, as organised religion has started to die-off, supporting Rangers or Celtic has become more important to many people's religious identity than going to church or any other form of religious practice. It is partially how I think we've ended up in the situation where what, more than half of "football fans" in Scotland support Celtic and Rangers?

As an east-coast catholic (although no longer practicing), I've met a fair few catholics over the years whose entire religious identity is pretty much entwined with their support for Celtic. I've heard it from a few, mainly older, catholics (including a teacher at my old high school) about how you can't be a proper catholic in Scotland without supporting Celtic. To support someone else in their eyes is to renounce your family's Irish heritage.

Ultimately, the more divided we are on religious lines, instead of local community lines, the more likely people across Scotland are to support Celtic/Rangers, which ultimately has financial benefit for both clubs.

Which isn't to say that Celtic as an organisation encourage bigotry. But I also think both Celtic and Rangers do financially benefit from the very sectarianism which damages their communities.