However, in Facebook's defense it's per-user per-transaction energy costs are going to be much lower than Bitcoin.
Did Ye Olde BBS support 1:millions broadcasting, and real-time viewing of high-definition video? Uploading and viewing thousands of high-quality photos?
Calling Facebook 'basically a giant BBS' is a lot like saying 'Oh, I could build Twitter in a weekend'.
Especially when talking about CO2 emissions absolutely everything is included, including plane trips and whatnot.
That comparison ignores the actual value add of Facebook and the fact that people are using it. Most BTC trades happen off blockchain and are powered by the servers of the market places and nobody really knows how much energy they use.