The key thing here is they think this is a fair trade-off because Safari asks if you want to open Zoom.
> This is a workaround to a change introduced in Safari 12 that requires a user to confirm that they want to start the Zoom client prior to joining every meeting. The local web server enables users to avoid this extra click before joining every meeting. We feel that this is a legitimate solution to a poor user experience problem, enabling our users to have faster, one-click-to-join meetings. We are not alone among video conferencing providers in implementing this solution.
I do not believe that this is a fair trade-off given that any website can act on this locally installed server.
EDIT: I think they need to be made aware that this isn't acceptable. My reply to their support team: I do not believe this is a fair trade-off - allowing any arbitrary web site local control of privileged software installed on my machine - because Safari offers a security prompt (specifically so that any arbitrary web site does not gain control of privileged software on my machine). I will be switching ~/.zoomus/ZoomOpener.app off, and considering other options until it has been fixed.