There are lots of examples of successful business out there who did not monopoly the market.
I'd also have to disagree that startups sell mostly crap they don't need or want. Uber & AirBnB definitely provides something valuable that most humans would appreciate of.
If you're talking about products such as Snapchat or Instagram, that's a different genre of product. It's a vitamin type of product not a pain killer.
> There are lots of examples of successful business out there who did not monopoly the market.
Such as? If you cannot eliminate competition within your given market, marginal profit will eventually be driven to zero. The internet amplifies this challenge because it is not geographically constrained (minimal transaction costs) and software amplifies this challenge because of zero marginal cost (creating massive economies of scale).
You can find more on this in the works of Michael Porter (http://amzn.com/0684841487, http://amzn.com/0684841460) and Peter Thiel (http://amzn.com/0804139296). Zero to One discusses how many seemingly successful non-monopolies are actually either monopolies pretending not to be one or non-monopolies that are not as successful as they portray themselves to be.