there is absolutely nothing wrong with walking forward if there is space available and you don't need to push or slide past anyone. i can see how it's annoying if someone stands in the aisle to block your way, even if they could have moved forward, but there is really nothing you can do about it.

i personally don't get the urgent need to stand up when the seatbelt light goes off. i'm not talking about people who need* to make connections, but those who must stand up, even though the door hasn't opened and no one is moving. while i prefer the window, if i have an aisle seat i will remain seated until it makes sense to get up. i mean, you aren't going anywhere, and why hit your head on the overhead?

*if someone in my row tells me they need to hurry, i certainly accommodate them to the extent i can. but if you don't say anything to me, i have no reason to believe you are.