Genesis 11:5 says this:
And the Lord said, “Indeed the people are one and they all have one language, and this is what they begin to do; now nothing that they propose to do will be withheld from them."
Clearly, God was concerned that Man's cooperation would allow them to do anything "that they propose to do." It seemed that for this reason alone, God elected to confuse them.
The next verse (Genesis 11:6):
"Come, let Us go down and there confuse their language, that they may not understand one another’s speech."
What was the source of God's concern here? Why was Man's cooperation to achieve this goal something that God felt He needed to quash?