It's not a sin to cooperate or to build cities and towers. It is a sin, however, to believe you can escape divine judgment through your own efforts. You can't save mankind from God by uniting, building higher than the mountains, or colonizing Mars.

God scattered mankind at Babel because their pride was going to lead them to repeat the crimes of their antedeluvian ancestors. Mankind's common enemy specializes in twisting a good idea into something evil. There are good kinds of unity and division that bring us closer to God and his ideals, but Satan encourages evil unities and divisions that pull us away into wickedness.

There are multiple Great Dispersions recorded in Scripture: Eden, Babel, Egypt, Assyria, Babylon.... Probably others. These were all meant to be restorative, to undo some perversion of Satan's.