That's how Bitcoin prices reacted to similar news from Facebook and Google. The reaction is diminishing as investors get used to the news, and hopefully more people will see that this is a positive move. Get rid of the scammers and the crap coins, and the market will become more robust, more appealing, and it will offer better value to new investors, which will mean more money coming in.
It is, to some extent, decentralized regulation.
RE: Twitter Ads Ban; another bully in the field