How to stop Chrome from warning me when opening many tabs?
Solution 1:
Here is your answer or lack thereof currently: Google Chrome Forum
Solution 2:
There is a feature request on Chromium's project page from 2012. The title is:
Don't warn repeatedly when opening 15+ bookmarks in one action
It was closed in 2014 with the status "WontFix" which means there won't be a built-in way to disable this warning.
As an alternative you could use Neater Bookmarks. You have to disable this option after installation
Bulk opening by middle-click or right-click+context menu on a folder works. No warning will be displayed