Every church that has broken away from the Catholic Church (in particular, the Protestant churches) broke away because of what they thought to be incorrect doctrine. Ie, there was a particular doctrine or indeed a whole set of doctrines that they disagreed with - and claimed had changed (as opposed to develop) from the time of Christ - and as the Catholic Church maintained that she(?) had it right, they broke away. Would everyone (Protestants included) agree with this?
Now one thing that I desire like almost nothing else is unity. Unity of Christians, that we (everyone who believes in Christ) can all be in communion with one another. I believe that a lot of different people from different denominations desire this as well. However, for that to happen, people from different denominations want the opposing denomination(s) (namely the Catholic Church) to back down on a particular doctrine or set of doctrines. But don’t you see that the Catholic Church can NEVER do this? The CC claims infalliblity; so if the Church backed down on even ONE doctrine, the entire Church would cease to exist. In other words, the gates of hell would prevail against the church that Jesus built (as the CC sees it).
The irony enters the situation when you consider what has happened to the churches that broke away from the CC. I’m not so sure about the Orthodox churches, but the Protestant Churches and the Anglican church have all had doctrines that have changed over time. Now they haven’t simply developed over time, but have actually changed! One example of this would be birth control. Now I don’t know if you could call birth control a doctrine, but it would seem that almost every church has backed down on this issue. Which church hasn’t? The Catholic church. Indeed, which church has never backed down on anything? The Catholic church. And this is entirely the reason why the Catholic church cannot back down on any particular doctrine, for the sake of unity.
With regard to the Orthodox churches, I think much of my argument would hold for them as well, but I guess you could say that they changed with the iconoclasm heresy; I’m not sure.