I've been guilty of multi posting lately, but it's not an attempt to drown out others.
Given the time difference between me and a lot of posters, I will re-enter a thread to find 4 or 5 pages of discussion has gone on.
I tend to reply to posts as I read them, rather than at the end, so I might post 3 or 5 responses, to different people, on different parts of the arguement.
Sometimes, you don't WANT to write a monster post out to 3 different people, or you want to clearly seperate or delineate your ideas, so you post it in seperate chunks.
If no one else posts in between, you get a multi post.
On my side, at least, it's not intended to be malicious.