How do you kill life steal stackers?

You burst them, kite them or cc them. If you can't do one of those things, do not try to 1v1 them.

You don't let them hit you.

Brings a little more light to champion select if you have to factor in a fed life stealing melee eh?

Ignite definitely helps. Depending on the enemy kiting them is always an option (Aatrox falls into this group), as is high burst if they're just going glass cannon.

Aatrox? Don't let him win lane and he's useless. For any lifesteal champion, never 1v1 if they're ahead. If you're anyone who can get use out of a Morellonomicon, build it for the Grievous Wounds. Take them out in teamfights, not smaller skirmishes. Also, distance is a good defense.

cuts atk speed/dmg which means less healing. cuts healing for its duration. if ur ap and they are low hp cuts healing.