Very interesting post and you made a lot of good points. However, I feel that the main explanation is very simple: Facebook does not want to be accused of being complicit in ICO/crypto scams that would inevitably be advertised on their platform.

The last thing Facebook wants is a repeat of the last crisis, which has seen media and politicians criticizing Facebook for letting Russian entities pay to bombard Facebook with ads and fake stories during the US elections. That was a huge issue that won't be soon forgotten, and I see them trying to avoid a similar situation here.

Facebook seems to have learned its lesson, and realizes that the short-term profit from allowing ICOs to advertise on their platform will only hurt their goals and reputation in the long-run. (Would you want a scam operation advertising on your site -- worse yet, to your loyal readers?)

I don't mean to blindly defend Facebook, but I think Zuck is trying to do the right thing for both society and his shareholders.