Purely upvoted content is (generally) less offensive to the readers. Purely downvoted content is (generally) more offensive to the readers. Mixed content 50/50 up/down is typically more controversial and so isn't purely offensive, but instead depends on who the reader is. Assuming a wide spread of audience (not a pre-silo'd audience).
I'm speculating here but I guess this is a tool twitter plans to use to reinforce silos, find content that's only "mildly offensive (I.E. Pimple Popping threads) and let people who want that to get it. Alternatively, they could find content that's downvoted by people who have a good "donwvoting trend" and upscale those downvotes. It's just more signal in their learning algorithms toolboxes.
IMO it neither helps nor hurts twitter's users to have downvotes it really depends on how they use it. I suspect people who are opposed to downvotes don't trust that Twitter will use the signal well. For example, the fact that YouTube took away "displaying" downvotes but not actually downvoting takes away power from users. They still get the signal but users don't. You no longer get signal on what YouTube is recommending to you.