Why do tanks do dmg?
Wtf is wrong with tanks in this game like ffs "Tanks" means the damage takers not users.... wtf.
Wtf is wrong with tanks in this game like ffs "Tanks" means the damage takers not users.... wtf.
if they did no damage then they would need to be near unkillable, even with a 5man team on them.
Tanks? 
Or
"Tanks"? 
http://efdreams.com/data_images/dreams/tank/tank-02.jpg
^looks like it does damage to me.
If tanks didn't do damage there would be no reason to focus them. Even in MMOs, the tanks that can actually deal damage tend to be the best endgame picks over others of their class. However, something tells me you're confusing bruisers with actual tanks.
Why do glass cannons take damage?
Oh, right.
Why does anyone do damage? Probably to farm and trade.
Top lane Tank? if you did not damage, to the creep wave, they will get pushed in, and they will get bullied by people who can farm better. (you might have gotten away without damage when Heart of gold was a thing. But right now, you can't neglect lane farm.)
Similarly, Jungle Tanks need clear speed. With out clear speed, they become under leveled compared to their fighter/skirmisher counterparts, which sets them up for being invaded.
The only tank who isn't worried about damage are the support tanks.
If tanks did no damage then the enemy team would ignore them and they wouldn't be useful.
Because you let them get close to you. There's somethig called kiting. Also,
are NOT tanks
Because the point of a tank is to draw enemy fire away from the backline. If they did nothing, there'd be no reason to attack them and thus they wouldn't be able to do their job without taunt effects (and you can't build an entire class on a single type of ability)
Because you are squishy. Try playing with your friends 5v5 tanky champions. You don't deal damage to other people who build tanky.