I am all for individuals making their own choices and doing what they consider is best for them. I am also very opposed to any form of intimidation - company, union, one-on-one BUT....
By working G Days one is only pushing the pineapple up ones own six (this fun is normally reserved for our managers).
If you work a G day you take overtime pay away from someone else. If the company pays too much overtime it becomes cheaper for them to promote. So by working a G day in the short term you cheat someone out of overtime and in the slightly longer term you cheat someone out of a promotion.
For each promotion there is a knock effect of another promotion and more recruitment - the whole food chain moves up a notch.
Don't work a G day unless it is the last day of the roster, the trip is a long one and you are already in overtime!