"Whether the doctrinal disagreement is hidden behind a pious lie or out in the open, the result is the same: a lack of unity."I would expand this a bit - the result is not just about the lack of doctrinal unity, but whether the Spirit is present in such circumstances.
If two or more groups are open about their differences, then at least they're both being honest and telling the truth. Disagreements that are "out there" and are being worked on can hopefully be resolved in a way that's in harmony with the Word of God. During this time, the Holy Spirit may also use this to open their eyes to a multitude of things they might not've learned otherwise.
"Brothers, if anyone is caught in any transgression, you who are spiritual should restore him in a spirit of gentleness."However, if the dissenting groups instead choose to cover up their differences and pretend that all is well - then not only is there a lack of doctrinal unity, but they've added lying and possibly hypocrisy to their list of sins. If the disagreements are of a nature that that one or more people should be expelled from the church but are tolerated instead, the letters to the churches in Revelations 2ff shows what God has said about such things in the past, and how He promised to deal with not only those who refused to repent, but those who tolerated these sinners in their midst.
I would also note that "doctrinal unity" in and of itself isn't a desirable goal, it's how that unity is accomplished, and what you are in unity with that's important.
“I do not ask for these only, but also for those who will believe in me through their word, that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me."If true unity is being one with the Godhead, then it can only be accomplished by the working of the Spirit in the people of God who believe in Him. "Visible" doctrinal unity means nothing when it's based on a unity with something other than God in the Spirit of truth. In such circumstances where people are lying to each other or themselves, the Spirit will be present as a convicting, not a unifying presence.
All quotes from the Holy Bible : English standard version. 2001, Wheaton: Standard Bible Society.