Basic courtesy costs nothing. Reclining during meals is not okay, and the stewards will back you up if you ever experience this problem. Also it is considerate to recline your seat slowly, in case someone has a drink.
But fundamentally, if both the seat in front of you and your own seat are both reclined, you will have a similar amount of space as when both seats are upright. A majority of people will feel more comfortable at this angle if not eating and drinking. People who complain about this scenario are illogical and behaving like territorial animals.