I don't argue about there being one church.
I'm not so convinced that Catholics have everything "right" about the "truth." Because we are human it is difficult to know if our interpretations are correct. Do we think Ratzinger is right about everything? If not, why do we assume that the early church councils were right about everything? A lot of those things were dictated by Constantine, who was only possessed of a very rough understanding of even basic Christian belief at the time he was alive.
I have faith in God, and the best place for me to meet God is the RCC. Because relationship requires more than one party, I need to do what I can to be as receptive as possible. I find it easiest to do that in church. I don't assume that the church is infallible, though I do not have any problem, and even like, what the church teaches about Mary (as the two times papal infallibility was invoked involved her).
Again, because of our humanness our understanding is limited. It is necessarily shaped by our experience, studies, personality. The U.S. black church's understanding of Jesus' mission is partly shaped by the history of slavery and subsequent oppression, for example. In the U.S. in general, a do-it-yourself kind of country, telling people to just go to church and trust councils and encyclicals to explain the truth is a pretty unrealistic expectation.
Just like it's unrealistic to expect me and many of my fellow and sister Catholics and Orthodox Christians to use only the Bible and our own (again, necessarily) imperfect interpretive abilities to understand that truth.
We do what we can. We do our best. Theology is not a perfect science. And I really don't think we will ever be "one church" again. We can be at peace with that and pray for each other, or we can wring our hands and get into flurrious conniptions about heresies.
No thanks. This is about God, who I frankly doubt gives two figs about much of this.
Peace and all good.
PS: did you notice the word "flurrious"? Did I make that up? Gee, I sure hope so!
We do what we do. We do our best.