OK? it still sucks even with headphones. Imagine the following scenario: You are in a meeting using your headphones as you suggest. A coworker a few seats away from you are in the same meeting using their own headsphones. When they talk you hear their real voice reach your ears first (this happens with even the best noise canceling headphones to some extent) and then you hear their voice with some delay from the meeting.
This is not about manners or headphones.
Better meeting software identifies when this is happening and they suppress the streamed voice of your coworker just for you.