Am I NOT supposed to recline my seat on an airplane? Is it frowned upon?

I’ve went on three flights in the last year, economy and have reclined my seat on all flights.

I have had comments from people behind me on all three fights.

I’d consider myself a nice person, I didn’t argue with them, I just explained it was a 5 hour flight and I’d like to be comfy and I didn’t know it was an issue.

Do people normally not recline their seats to give others more room? I thought everyone reclined their seats lol