"But they do nothing for the market."

Well, traders provide some liquidity to the market. It takes both traders and investors for the market to work.

IMO, there is no right or wrong between "trading" and "investing". It's purely a personal decision. If you want to be an "investor" and think you can out perform that way, go for it. If someone else wants to be a "trader" then more power to them... Everyone is free to put their capital at risk in the way that best suits them.