You're speculating but that's an empirical question; it could go either way. What makes you think downvotes encourage toxicity? What's your evidence?
I have no
research into it of course, but speaking from personal experience, innocent comments I make are often downvoted without reason. These comments dont detract from the discussion at all, but, in some cases, are simply questioning the parent comment, or asking them for more information. The downvoting discourages me from continuing the conversation, especially because
A) The mob mentality of the site sees one person getting downvoted, and continues to downvote that post / their other relevant posts. Seeing the initial negative marks kind of steer it in the direction that others will continue to take it in.
B) The downvoted posts are often coupled with heavily upvoted posts from other users, which give off this sort of "you are wrong and i am right" vibe.
Often because of this, I end up just dropping the conversation, knowing everything I say will get buried without any real reason.
IF, for example, only upvotes were allowed it would seem to me as more encouraging. If you don't agree with a post, you ignore it, and do nothing, OR add to the conversation. If someone comes along that agrees with your post, they can choose to upvote it. Seeing a negatively voted post brings with it negative connotations, when they are often not necessary. Posts that are spam or abuse should be reported, rather than downvoted.
Again, all beliefs based on personal experience. It may or may not work. Another possibility is simply hiding the score to remove the negative implication the post has adopted, and simply have the posts ranked/ordered based on their hidden score.