Bitcoin is an extreeme example of something that's built in to markets - you're trying to guess how much someone will be willing to pay for an asset and this leads to natural bubles - it stops being about determining the value of something and it starts being about playing the market. You can spin whatever rationalizations you want arround it - bitcoin is the most degenerate manifestation of this. If you find a market full of idiots willing to buy bullshit and pump it's valuation, if the idiocy is strong enough that it wont easily go away, you have a really good incentive to join in and prosthelytize to grow the bubble more, even if you don't beleive it - just the fact you beleive there will be more idiots buying in makes it rational for you to get in.
And if you skip out on trading on it you'll be punished with below avarage returns.