I've been called back to deal with passenger disputes and seen laptops destroyed by a reclined seat. It was open and when the seat was jammed rearward, the laptop screen got stuck in the clasp for the table tray and the pressure was too much for the laptop to handle. Yes, the seats are designed to recline, but the seats aren't built by the same people that decide how many seats can be crammed into an airplane. If someone wants to work, I agree, they should be upgraded to business class. But the moral of this story is recline slowly.
It's easy to say "I paid for it, they can pay for an upgrade," but if you think about it, should someone that's born taller be forced to pay extra to travel just because of their genetics?
Air travel, like most of life, goes a lot smoother if we show some courtesy. I'm 6'2". I've been on some planes where a reclining seat in front of me just didn't work. Now as a pilot travelling on flight benefits, I can usually get a free upgrade to another seat, even one inside the cockpit, but sometimes the plane is literally full. I have no problem if people in front of me want to recline if everything fits. But sometimes it doesn't. That's not their fault, but it isn't mine either.
It SHOULD be about the greater good, or the lesser harm. You want to recline to go from mild discomfort to milder discomfort. The person behind you may go from mild discomfort to extreme discomfort when you do. If the person behind you is 5'2", absolutely, you have the right to recline. But when I'm called back for a dispute and I see some guy with 6 empty whiskey's in full recline squishing a 6'5" guy who is literally having his knees compressed, I tell the guy to quit being an ass and put his seat up. Airlines will do what they can, including moving people, but even when there are empty seats, moving people isn't always feasible.
Don't be an entitled prick. Use common sense. You don't gain much from reclining, are you really going to start a fight about it? On an aircraft? Where we've seen what the result of fights can be? If it's feasible to recline, fine. But if the person in front of you is reclining and you're physically able to move, deal with it. If you reclining causes someone physical pain, don't. A little understanding and selflessness goes a long way.