If I buy or sell an option I accept a price that someone else agrees with. We cannot know the reaons for their side of the trade. If I open a trade someone else may be closing a trade or leging in/out. We don't know -it's irrelevant, so no it's far from a zero sum game as there are X amount of players not 2.
all trading is a minus sum game. the brokers and the SROs are going to sweep some from the table. the market maker is trying to make his bit, too. now that said we do get a nice electronic world to trade in. that infrastructure is worth a great deal the back office operations is first class, in my opinion. poker is a zero sum game.