Does that actually happen on Facebook? I've seen it happen on Twitter multiple times, and across countries, but I don't associate Facebook with raids and targeted harassment.
It feels like Twitter's user base is much more radical, and the focus of the product on instant public messaging might add fuel, while Facebook's group system generally limits the spread and seems to be more geared towards asynchronous sharing (+messenger, but that's more of a chat, not public).
Facebook is more private (as in you don't follow random people on Facebook; you are either friend or not), so it doesn't happen as frequent as it happens in Twitter, not in the same degree.
It feels like Twitter's user base is much more radical, and the focus of the product on instant public messaging might add fuel, while Facebook's group system generally limits the spread and seems to be more geared towards asynchronous sharing (+messenger, but that's more of a chat, not public).