Nobody reasonable would say that tanks should do absolutely zero damage. That's just silly. However, dealing damage shouldn't be nearly as big a priority as it presently is.
If I was standing in front of a cyclops the size of a building with an uprooted tree in its hand, my first thought would not be to throw my shield to the ground and try to poke it in the jugular. Especially when there's 4 other people in my party who are (A) infinitely more efficient at poking it in the jugular and (B) aren't about to get smashed with a freaking tree

In my opinion, the best compromise would be to rebalance the tanks so that achieving max DPS also achieves max survivability. That way you'd still have incentive to optimize your deeps without abandoning what the role is supposed to be about.