@htilburgs This is exactly what I‘m trying to prevent/workaround with this tutorial.
Using a public calendar URL allows anyone to see your calendars without any authentication at all. This way your calendars are open and accessible by anyone who knows the URL. (URLs can be crawled by machines ;))
This here is just a secure method to sync your calendars.
If you don‘t care about having your personal life available to anyone or anything, it‘s your business.