...My take now? Making quoting easy is not a major vector for abuse or toxicity, and there are benefits.
That’s not to say that the quote tweet can’t be abused. Every form of tweet/post can be, and is.
The toxicity was already there, thriving in replies in particular, and amplified in all its forms by the algorithm, retweets, and hashtags.
Did the quote tweet make it worse? If it did, it may not have been by much - and in a couple of datasets, it improved civility.
2/2