* The core issue: professional startup investors rely on (a) relatively large portfolios where (b) the winners succeed so outlandishly that they pay for the losers. Savvy investors --- most investors aren't savvy --- intuitively understand (a), but not (b), and you have to fully grok both concepts to make money from startup equity, because it's an equity class that is almost by definition way more risky than normal stock.
In particular: the math on "value investing" probably just doesn't work with startups.
* We have a distorted view of the win/loss ratio of startups, both because so many exits are in fact not net-positive for investors, and because so many startups fail without actually telling anyone (the lights are on, but nobody's home).
* There's probably a market-for-lemons effect bound to apply to equity-crowdfunded startups. Professional investors compete for dealflow. The whole system is designed to route the most lucrative prospects to the pros. There's no countervailing force that routes good deals to mom-and-pop investors who can't offer anything other than incredibly complicated cap tables to startup operators.
* A negotiated event that strikes 25% off the value of a publicly traded company's stock is a major news story (and a likely class action suit). But an event that dilutes startup common stock holders down to 50%, 25%, or 10% of their original valuation? Or that wipes it out entirely? In startup parlance, that's called Tuesday.
* Startups aren't like Kickstarter projects. Crucially: people put money into projects on Kickstarter, not teams. Professional startup investors do mostly the opposite. A project page on Kickstarter is a good prospective for a Kickstarter project, but it's not even close to a prospectus for a company.
Retail investors should get exposure to startups through carefully managed funds that own lots of different startups, not by trying to pick individual winners themselves.