Things don't become popular when supporting them doesn't raise anyone's status. This goes from movies, to clothing, to dietary choices, to political views. People associate themselves with things signalling an identity they're comfortable with.
If you want altruism - or whatever your best kept secret is - to become a fad, then you need it to become fashionable. You aren't going to reason someone into giving tons of their money away. You need to first make them feel as if the implications for their social status will be beneficial.
More effort should be placed on making altruism the cool thing to do, rather than merely the morally right thing to do. If it isn't attractive for self-interested reasons, then it will not become popular whether it is considered to be morally superior or not. If it is attractive for self-interested reasons, then it will become popular whether it is considered to be morally superior or not. This could even be the most important challenge facing effective altruists.