Shrug.. there is also the basic human decency of not flopping your seat back, as if you expect the person behind you to be doing your dental work.
I have zero issue with people who recline their seat a bit. Something I think a lot of people don't consider: the distance an airplane seat can recline is pretty much the same as it was 30 years ago. However the amount of space between seats has been shrunk, and shrunk, and shrunk, such that the same recline long ago, is now much more invasive to the person behind you.
I always try to have faith that people generally have consideration for each other... and then I go to an airport and that illusion is shattered..