And if someone could prove that florescent lights CAUSED skin cancer, would you say "tough, the lights were florescent when you started?"; or would you expect the gov't to step in and force the business to go to some other form of lighting? Same thing.
For example; X-Rays used to be found everywhere. Way back when, you used to buy shoes, and put your foot betweeen a phosphor tube and an X-Ray tube to see how your foot fit inside the shoe. Really and truly .... Then they discovered that people were getting messed up by the radiation, and they forced the shoe stores to remove the expensive X-Ray Shoe Fitting machines. Scares the crap out of me, cause I'd have irradiated myself to death, just to watch my toes wiggle for hours.