Lets just add a nice juicy button here to unsubscribe from all of those addons. Still slow, but not as slow as doing it 1 by 1.
Ever reinstalled Garry's Mod only to find that you have subscribed to 2000 addons? Sick and tired of unsubscribing one addon at a time? Well have I got a solution for you?
This userscript was made in just 30 minutes, and will add a button on your subscribed items page. To use, find your subscribed items in steam, and click on the new link added to the right that reads "Unsubscribe from everything you see here".
This script can only unsubscribe you from addons that are currently on the page. It cannot detect all of your addons at once at this stage.