My interpretation pg's plan for a comment endorsement scheme was that it actually encouraged downvoting for disagreement. If garbage comments are filtered out

My interpretation pg's plan for a comment endorsement scheme was that it actually encouraged downvoting for disagreement. If garbage comments are filtered out through endorsement, then, if you view of downvoting held true, there would not longer be any need for downvoting and the downvoting button should be removed. This is not what was proposed. If only quality comments make it past the proposed endorsement filter, and the downvote button continues to exist, then the only purpose of downvoting would be to express disagreement.