I think a huge percentage of DV here is fuelled by hatred. Some of them do it, because no one would do anything to them and they enjoy making that person feel sad. Some of them hide under the idea that it's the right of expressions and many reasons.
I was targeted a lot, and I can tell firsthand. However, I just wanted to clarify that it doesn't really mean being silenced.
I don't think it is huge, but there are people who enjoy making others feel bad. Sadism is even more prevalent online than offline.
But I don't think they are the majority of the DVs. I'd say the majority come from DV trails, where account holders don't even know who they are downvoting or why.