At the end of the day, "casual" games are typically low quality affairs that take scarce resources away from other games that are either made or could be made. Therefore gamers who desire quality lose out from "casual" games.
You're not going to convince gamers that casual games are a good thing, primarily because whilst they are involved in the industry as consumers they have no underlying connection to it, they don't benefit from the success of casual games because they don't have a financial stake in the companies making them.
Pretty simple really.