I'm a passenger, but no FAs have chimed in yet and I've spoken to some about it.

When reclining would be an inconvenience, such as during mealtimes in economy class, they will ask passengers to raise their seats so that the people behind them can eat more comfortably.

At other times, the seat recline button is there for the passenger to use. Courtesy includes checking in back before reclining to avoid knocking things over and reclining slowly, but they can't enforce courtesy.

As for my own opinions - that's what those other threads are for.