There is an option to change the default, but what about the existing nodes? Is it required to go through every existing node in the content type and turn off comments, or is there some way to do this globally?

Comments

Go to disqus settings in administration and under "visibility" put a check mark next to the node types that you want to include disqus on and remove it from those you don't.

Thanks. I was able to figure that out, but the problem is, if you want to remove the drupal comments from all of the existing nodes you have to manually go one-by-one and disable comments. Am I missing something?

Status:Active» Fixed

I just came across the same problem and posted my workaround in a little tutorial here http://runeforge.net/tutorial/bulk-update-comment-settings-on-existing-d...

Status:Fixed» Closed (fixed)

Automatically closed -- issue fixed for 2 weeks with no activity.