As far as literally illegal content like for example abuse material goes, Facebook like any other business has an obligation to make sure it doesn't facilitate it. That's no different than any old fashioned offline business having to make sure activity is within the law.
i'm pretty sure both the article and the person you replied to are talking about verbal abuse as opposed to illegal content. and no, websites DO NOT have an obligation to make sure their content is legal. that's your own misconception as well as many judges but at the end of the day forcing people to chase intractable problems is always wrong and naive. the root problem here is that it's possible for content to be illegal, along with billion dollar brainwashing profit oriented prosecution business that made you think this is a rampant problem (it isn't).
this article is uninteresting clickbait by fake grassroots webshit crypto company that can be cracked in 2 seconds solely because their trusted code base is hundreds of millions of lines of code in 7 different languages including C. we are just here to cringe at yet another UK police state episode more than anything particular the article stated