I disagree, that conclusion is not foregone. To win a lawsuit like this, you’d probably have to show that the companies acted in bad faith, and didn’t really try to stop the terrorists from using their platform to aid in their criminal activities.
If the company can show they acted in good faith, and simply didn’t have the necessary resources to catch everything, they should win the suit. The only sites that really need to be worried are ones where terrorist-related stuff is being reported, but nothing is ever done about it.
That appears to be the heart of the case and the exact case the plaintiff is prepared to make.
“For years, [the companies] have knowingly permitted the terrorist group ISIS to use their social networks as a tool for spreading extremist propaganda, raising funds and attracting new recruits.