Everyone knows airplanes have little room. I totally understand people feeling they ought to be able to use their seat as intended and recline to get a little more room or for pain issues. The recline function was designed to allow people to recline... It was also designed at a time when seats weren't so close together so reclining didn't impact others the way it does now. Airlines started reducing the space between seats to add more seats and make more money, but didn't adjust the seat recline ability with it to compensate for the effect it would then have on those sitting behind a reclined seat.
I do forsee more airlines going the way of Spirit and Fronteir and eliminating manual seat recline by making new seats that have a minimal pre-recline built-in. Delta has already been reducing the recline on their seats over the last year.
While I understand people wanting/needing to recline, it would be nice if everyone was just a little more considerate about it. Everyone knows that the tray tables are attached to the back of the seat, so before reclining, look behind you and see if someone's using their table and you're about to smash their laptop or knock over their drink. Give them a heads up so they can adjust their stuff. If they know in advance, they can *maybe* adjust their own position so their knees aren't being rammed into unexpectedly causing them pain. If someone does ask you not to recline as it's causing them pain, see if you can come to a middle ground with minimal adjustment or ask the flight attendant if there's somewhere else one of you can sit (and that point goes for both the recliner and the person sitting behind- either one can take the initiative and ask if there's another seat you can relocate to).
People should be able to use all functions of their seat, including recline if available. Likewise, people should be able to use all of the space they paid for between seats without having that space reduced by the seat in front of them digging into them and causing them pain. People should also be able to use their tray tables as designed without having their drinks knocked off or their stuff smashed.
Unfortunately, with the way the seats and spacing is currently designed on many aircraft, not everyone can have full use of what they paid for at the same time. If you recline, you are going into the space another passenger paid for, potentially putting them in pain or affecting their ability to use their tray table. If you ask someone not to recline, you are limiting their ability to use the features of the seat they paid for and potentially causing them to be in pain.
If passengers can't behave considerately and try to work out this issue themselves (again, someone wanting to recline and the person behind them coming to an agreement or asking if you can move), then the airlines will make more efforts to solve this problem. As noted above, some already are making changes and more will if it continues to be an issue that flight attendants have to intervene in or if it causes disruptions in flight schedules. It's going to be reducing or eventually eliminating the recline feature, going to the limited pre-recline in more aircraft, or redesigning the seats to take the recline from your own leg space.
That being said, for those who want/need to recline, would you be satisfied with no longer having the ability to recline, having seats that only have a small pre-recline, or having your recline ability taken from your own leg space?