Originally Posted by
Sto_Helit
I was basing my suggestion on the similar situation where you may have 'active' guild members who haven't completed guild quests but still get the rewards for the effort of the rest of the guild. I think this can be a source of resentment when people feel they are 'carrying' other players. Therefore if you have opt-in you are making an active choice to do the event. People who choose to make an effort get the rewards.
It may be that you also need an opt-out or drop-out button for people who find they can't do what they signed up to because real life suddenly got in the way.