Why does the enemy being masochistic make tower focus me???
Not like I can turn it off... 
Not like I can turn it off... 
Oh no, thornmail has a downside.
NOOOOOOOOOOOOOOOO
That's part of the price of the item. It's the same thing as having a Sunfire, you have to take it into account when going under an enemy tower.
But it really shouldn't have an effect on towers, it didn't before they reworked it.
What really threw me off was the old deathfire touch. The constant surprise tower aggro made that keystone go straight onto my never gonna do it again list