Most times I find Falmer, I use 100 sneak and invis potions and just walk on by. I know it's just a game but I hate the idea of a whole race just.. enslaved and treated so badly. Like Karliah said, the Dwemer were cruel indeed.
They are agressive towards you for a reason, give em some love and spare them. :3
I apply my same logic towards the Falmer as I do bandits, If not more so.
In the long run Falmer are going to kill more people, and if you kill them, you save people in the future. If I ever met one who was non-agressive, i'd let it live, but as it stands every one I kill is doing the world a service.
That being said, I wouldn't of killed the ones in blackreach if they weren't keeping slaves, they couldn't get out and technically I was invading their home, so I did have reservations about that.