The problem is idealism.
> “I was very excited about the opportunity that Twitter represented,” Wetherell said, noting that he initially felt the retweet button would elevate voices from underrepresented communities.
The problem is that it didn't register to him, or anyone, that "racists" were an "underrepresented community", as were sexists, misogynists, homophobes, anti-intellectuals, quacks, and so on. When attempting to give a voice to minorities, they gave a voice to all "minorities", including people who had minority opinions. The idealism came in the form of expecting that these tools will, by default, be used for good... it wouldn't surprise me that people in the tech community, who have often come from privilege or at the very least live within privileged bubbles, are naive about what people are really capable of.
"A rising tide lifts all boats..." unfortunately some of those ships are full of pirates and disease.
It's sad, but you really need think about these things from a jaded and cynical perspective when building them, it's unfortunate that there's been a long crusade against cynicism. Being optimistic and feeling optimism about the world and humanity leads to problems like this.