Next time the market is in melt-down mode -- like it was just beginning to be last October -- watch how wide the spread gets. Sure, if you're somebody willing to take any price in a fire sale you can get out of anything.
My original reply was intended to point out that what was the top article comment at the time completely missed the point. Cuban is arguing that severe liquidity restraints are bad, especially so for small time investors. For scenarios like you describe, public exchanges aren't perfect either, but they are very, very good at facilitating near-instantaneous liquidity and they strictly dominate the current set of private crowd funding vehicles.