I think this is overstating the case on a few different fronts.
- You don’t own your URL. You rent it. What you rent can always be lost or taken away from you.
- This can happen to paid URLs in many ways. Sometimes people miss their payments and lose control of their domain names. Sometimes the top-level domain itself might be imperiled or stolen. Sometimes the top-level domain can fall into the hands of a group you refuse to do business with, such as the Taliban. So while renting a domain name can be helpful overall, it’s not a guarantee or a perfect way to avoid all risk. (Edited to add: see also What happens to TLDs when their country stops existing?)
- Taking measures against link rot isn’t the same as ownership of a blog and its posts. If you keep a backup of your blog and get booted off your free web host, you still own your posts and can still reupload them elsewhere. It’s a pain, of course, but I think it’s worth making a distinction between link rot and data loss.
Don’t get me wrong though, if you want to restrict the scope of Blogroll dot org to blogs with rented domain names, I’m all for that. Many of those blogs are indie blogs that don’t benefit from the built-in platform search functions on sites like Tumblr, Wordpress, Substack, etc., and so they could use the extra boost.