Basically, this is a request to undo r34769 (T3505: Spam blacklist, if match, check previous version and accept if URL present there).
Allowing blacklisted links to remain in the page is bad for a few reasons:
- Allows duplication of blacklisted links (T16114: Duplication of blacklisted links already in page text is possible)
- Whitelisting is the correct way to use blacklisted links, per T3505#56366
- Shifts the burden to remove blacklisted links onto a small team of users. Previously, the load was distributed since anyone trying to save a page with the link couldn't do so
Concerns about reverting vandalism (T3505#56358) are valid, and should be addressed; see T17450: Rollback should be unaffected by the spam blacklist to make *rollback* (only) exempt.
- T16114: Duplication of blacklisted links already in page text is possible
- T67447: Site was blocked but IP was still able to add links later (due to link already present on the page?)
- T15569: SpamBlacklist sometimes allows adding blacklisted links
- T71775: Spam blacklist disallows addition of blacklisted links which are already there