Earlier quoted context omitted.
What's wrong with it? Seems like a perfectly normal metric for coins just like for stocks and bonds.
Because I can create a cryptocoin with 2B tokens, sell one coin to friend for $100 and have a $200B market cap. It's got nothing to do with reality. Anyone (literally) can create a $200B market cap coin by forking a github repo.
https://signalvnoise.com/posts/2585-facebook-is-not-worth-33...
It's worth almost 17 times more than that now. Market cap is not a perfect metric because it doesn't capture the depth of the market willing to buy but coins don't make that any different.