ICO's being legalized doesn't mean social media platforms will lift their crypto related ad bans, especially because of the fact that it concerns crypto in its entirety they don't want to get exposure on their platforms, and not just ICO's.
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Yes, indeed, they're not going to lift them as soon as they're legalized, it's going to take some years, not doubt about that.
Legalizing ICOs will open the possibility to whitelisting those ads, don't you agree? In this current
shady state they will
never bring the ads back thus the interest will decrease and we'll continue to be on a bear trend.
The official reason behind the ban was that ICOs and crypto in general is a shady business where people can loose money. As coin telegraph said it here:
https://cointelegraph.com/news/big-tech-are-banning-crypto-and-ico-ads-is-there-a-reason-to-panicFB:
“We want people to continue to discover and learn about new products and services through Facebook ads without fear of scams or deception. That said, there are many companies who are advertising binary options, ICOs and cryptocurrencies that are not currently operating in good faith.”
Google:
"We don't have a crystal ball to know where the future is going to go with cryptocurrencies, but we've seen enough consumer harm or potential for consumer harm that it's an area that we want to approach with extreme caution.”