I don't completely agree with the "sadly"...
By and large I see the various denominations as an inevitable consequence of us mortals coming to grips with God and His Word. The existence of denominations is one of the things that convinced me that the Gospel is true.
I reckon that proto-denominationalism is mentioned in 1 Corinthians 11:
"I do not praise you, because you come together not for the better but for the worse. For, in the first place, when you come together as a church, I hear that divisions exist among you; and in part I believe it. For there must also be factions among you, so that those who are approved may become evident among you."
I'm not saying that some denominations are wrong and others right. But that divisions exist so that the truth can be relieved though evidence. Notice that Paul says there
must be factions. Not that there
are factions, and we have to deal with them, but that factions
must exist: Denominations are part of God's plan. One could argue that I'm reading too much into this, but the fact that denominations exist might weigh on my side.
It is sad, however, in the way that denominations sometimes interact. I'm London born with Irish blood, so I know first-hand what denominational conflict can look like when both sides forget that it's supposed to be about God and His Christ, and not about planting bombs.
I am encouraged by more recent trends for Christians of all denominations to look around to see what might be approved by God in eachother's tradition. Which is one of the reasons why I identify as a post-evangelical.