It's as major an issue as not being able to see the blue sky because of the air pollution. Sure, the light won't give you cancer, but it's still pollution that should be avoided.
There are studies that suggest that city lights increase people's risk of cancer. Sleep studies have shown that exposure to blue light suppresses melatonin [1]. Studies with lab mice have shown that melatonin suppresses tumor growth. I don't know how solid the science is on this, so take it with a grain of salt.
