Success is not validation of an idea and we should be ashamed to think so.
Cigarettes are one of the most successful consumer products on earth. Inhaling a lungful of carcinogenic smoke several hundred times a day is undoubtedly a stupid idea. Tobacco has made a small number of people incomprehensibly rich, to the great detriment of humanity.
Personally, I think nearly all of these 'social' startups are bad news. Not as bad news as a lung cancer epidemic, but bad news nonetheless. I think they feed a culture of passivity and attention deficit. I think they fragment human interaction into the smallest possible dopamine-inducing units. I think they're essentially Skinner boxes in disguise - apps that dress up an intermittent schedule of reward as meaningful activity.
The startup culture talks the talk about "changing the world", but in truth most of us couldn't care less so long as we get our next funding round. For every Watsi, we have a hundred bullshit companies with bullshit products, providing yet another means of idle distraction for indolent westerners. We can hardly distinguish between what is worthwhile and what is popular or profitable.
Indeed during the recent dotcom mania a bunch of quack business writers suggested that the company of the future would be totally virtual -- just a trendy couple sipping Chardonnay in their living room outsourcing everything. What these hyperventilating "visionaries" overlooked is that the market pays for value added. Two yuppies in a living room buying an e-commerce engine from company A and selling merchandise made by company B and warehoused and shipped by company C, with customer service from company D, isn't honestly adding much value.
Try not to become a man of success but rather try to become a man of value.