I fly a fair bit, and I've witnessed this argument a few times - twice the flight attendant had to intervene, and both times made the decision based on what was most reasonable/expected for all the passengers (the most recent, the person in the window seat wanted the blind open but because it was very early in the morning and in the designed 'sleep' period, they ruled it should stay shut). It's not rude to adjust the blind to your liking, but I think it's important to at least be aware of others' needs and what the norms are. Imo insisting on having the blind open at 3am in what is supposed to be a sleep period, subjecting everyone in that part of the plane to blazing light, is rude; doing the same thing at 2pm when one person wants the blind closed so they can nap is not rude.
We recently went to Europe. On the way there, it was night time, so the plane was pretty dark. Imagine the shock when in the middle of the 'night', but bright AM inflight, someone across from us decided to open their window shade. Most of the people woke up because of it.
On the way back, it was daylight. It was an older plane, so didn't have individual entertainment screens, but the ones that hang from the ceiling. Everyone, literally everyone had their blinds closed except for one youngish girl a few across the plane from us. It made seeing the movie and sleeping very difficult. I felt really sorry for the girl beside her.
I didn't complain about either incident, but made a mental note to ask about it here. I personally thought they were rude since everyone else had their blinds closed and their desire to have open affected so many people on a long haul flight during designated sleep/quiet hours. Sometimes, I think, you have to go with the flow.