Some of us are "in game" for hours upon hours, whether we're actively playing the game or not. We're available to be contacted, etc. A substantial portion of our play is idle. We "activate" when someone contacts us, shows up, etc.
I'm often working in another window until my mud window chimes a bell letting me know I've been Way'd or that someone has arrived in my room, etc.
Not everyone can do that, or wants to do that.
I do agree with both sides of this. You're going to get more out of the game the more you play. You're going to be able to reach out to a wider range of other people, be available for more activities, etc.
However, it's not mandatory for enjoyment. That all depends upon your individual tastes.
Where I do get annoyed is when I'm in organizations where leadership puts a hard clamp on all of your activities, literally demanding you talk to nobody, do nothing, go nowhere unless they are present, and then that leadership is literally never present. I've seen entire weeks go by with no leadership present, even though that leadership has mandated you have no interaction without their approval. I generally try and quit those organizations, or I end up storing. Sometimes this "do nothing" state is canonized, but other times it's just the whims of those particular leaders.