I have no problems sleeping with constant inputs such as light from a seatmate quietly reading War and Peace.

Perhaps because I would have greater respect for her intellect than for one blasting music through a headset.

Earplugs and eyeshades can usually be obtained in most long-hauls, even if not automatically provided.

Not everyone has the ability to fall asleep "at will", and many prefer to sleep with a light on. There's no excuse for a lack of common courtesy for one's fellow ravelers, but there's also no room for intolerance of someone else's basic needs either.