Imagine a VC that buys 50% of a company for $50 million, 
  for a $100 million post-money valuation. If that company
  then sells for $75 million, the VC gets more than 50% of
  the $75 million. The VC gets his or her $50 million out
  first, and then half of the remaining $25 million ($12.5
  million) for a total return of $62.5 million. The common
  stock holders split the remaining $12.5 million.

  That's a 1X liquidation preference. ...

  A 1X liquidation preference isn't unfair. The people who
  bring the capital should have some protection.

I was at a startup in the late 90s and discovered liquidation preferences. I agitated to get them dropped from the B round, succeeded, and the VCs then scrapped them. Which saved me from exactly this fate.

I don't agree that even a 1X liquidation preference is "fair". VCs are taking a risk, that is supposedly their business model. Reducing risk on the backs of the people sacrificing their personal lives doesn't strike me as fair at all.