Facebook does not want to be accused of being complicit in ICO/crypto scams that would inevitably be advertised on their platform.

I still get ads for MLMs, Homeopathy, scammy "self help" ebook courses and dropshipping scams. If Facebook gave a shit about it's reputation with its audience, they'd censor those first. Sure, the ICO craze and the Bitconnect kerfuffle and lawsuits being thrown around are not making for a happy market to be in, but Facebook is leaving a pile of money on the table because it doesn't want scammers defrauding its users? Come on... If at all, they're trying to look like they give a shit with this ban on crypto ads.