So you want less people to play tanks? Gotcha. Since it seems as if you are not happy with the current DPS focused meta which is fair, I suspect though if SE forced a more defensive play style by the removal of stats many tanks would simply not play tank.
Let's be real here:

1) tanks are already the hardest to come by of the three roles
2) anyone who was really obsessed with outputting as much damage as possible would play... a DPS job.

I'm sure the primary reason a lot of them play tank is for the faster queues and "ins" on content, and this would not change if they forced tanks to be more turtley.