Aren't we straying from the ecumenical idea a bit? After all, we should be discussing Mary's Magnificant from everyone's view point if we're going to have an ecumenical discussion. That means we should keep to what precisely is written to satisfy us wacky Protestants. Leaving the pages of scripture to venture into Church's teaching is voyeurism.
Now if you want to discuss the infallibility of the Church, I would suggest that is not an ecumenical discussion.
“Contrasting of beliefs or even criticisms can be made without provoking hostilities.”
You state a belief common to a tiny minority of Christendom. I point that out. That is fact.