Here are some sources:
https://www.cnbc.com/video/2018/06/26/facebook-reverses-ban-on-cryptocurrency-ads.html
https://cointelegraph.com/news/facebook-s-crypto-ad-ban-reversal-power-play-gets-their-own-news-stuck
https://www.recode.net/2018/6/26/17505876/facebook-cryptocurrency-ads-bitcoin-ico-ban-reversed
It is a good thing to implement this type of change for bitcoin society. As time goes by, it is about the security that we are trying to improve witg bitcoin. Well then, its reliability is already check, though if you are to count its cost then some will not bare with it. So, so far, this is a good thing to be implemented knowing that Facebook is an influential social media application.