Zipper merging is good when a lane ends, but that's not what I'm talking about. Attempting a zipper merge into a turn lane at the last moment is a really bad idea, because by attempting to do so you will block a travel lane that other people will want to use for going straight. This slows them down at best, and causes crashes if you're unlucky.

Merge at the last moment when your lane ends. Do not merge at the last moment when you need to get into a turn lane. These are different scenarios.