If you recline your seat without taking stock of anyone or anything around you, it's like manspreading, putting your bag on a seat, or sticking your legs out on a crowded subway. Yes, you technically can do this since you paid for space like everyone else and you were there first. Sure,
it is strongly suggested that it might not be polite to do these things, but there are no official rules that state you have to be polite.
If you continue to recline your seat after either noticing or being informed of the pain/discomfort it is directly causing to the party behind you, it suggests a lack of empathy. It would be like stepping on someone's foot on the hypothetical crowded subway train, then refusing to move your foot for the duration of the ride because it is more comfortable for you to remain as is. No one is going to die or lose a limb from that foot mash for 20 min, but you're
still an asshole for not moving.