I feel like the dril tweet of "drunk driving may kill a lot of people, but it also helps a lot of people get to work on time, so, it;s impossible to say if its bad or not," applies pretty well to my feelings on Twitter.
It actively causes me psychic damage. It is designed to hurt you and make you addicted to the pain it causes. The principle of "internet public square where people can go and talk to one another with minimal boundaries" is broadly neat, but it's unworkable as long as it's run by private companies with a for-profit plan, especially with minimal regulation or oversight, and I'm not sure the socioeconomic system we live in currently has the will to actually make an accessible online public square without it getting undermined by profit motives.
It also provides a common touchstone for society. If you work it right, you can use it as a megaphone for important issues that would be ignored otherwise. It communicates news rapidly and sometimes usefully in disaster scenarios. It lets otherwise geographically isolated communities grow and develop.
I don't know. I'm not an expert on social media structures, or organizing, or how to regulate mass media. so, it;s impossible to say if its bad or not,