We did try to reduce the permissions as much as possible, but I believe at this time every permission is required by some feature. I get your point though, and I'll try to see what else we can do in this regard.
As mentioned elsewhere in this thread, just to be clear we don't log every visited site (or log browsing in general); the only time data is added to the database is when the user actively adds a comment/creates content.
Currently we send the URL as is; its only stored though if you are writing a comment or sharing the site with friends. I do like the hashing idea but ultimately when someone does leave a comment or share it, we do store it without hashing so later users can filer it and so on. Please let me know if I misunderstood your question!