Comprehensive doctrinal unity has never been realized, but both sola Scriptura and sola ecclesia have produced unity to a limited scope. But the essential unity of the Spirit (Eph. 4:3) is what only those in the body of Christ can realize, which is greater than their differences as they walk in that Spirit.
This was the subject of a recent debate: http://www.freerepublic.com/focus/f-religion/2992144/posts?page=392#392
What Catholics simply cannot wrap their minds around is what Paul refers to as *disputable matters* in Romans 14. They think that unity demands unswerving adherence to one specific doctrinal position on anything, but the beauty of the unity of the Spirit, is that any believer can have communion and fellowship with any other believer in spite of differences in worship style, how communion is served, whether women should wear long dresses and long hair, whether you speak in tongues or not, what day of the week you worship, whether you eat meat or not, whether you're OK with an occasional beer or glass of wine or not, and so on.
We've learned to relax over things that are not critical in matters of salvation. The foremost unity comes from salvation by grace through faith in Christ.
Almost everything else is incidental and Catholics simply cannot tolerate shades of gray. With them is has to be black and white, period. No questions asked.
The freedom found in Christ is simply beyond their comprehension.