Some web developers think that disabling password autocompletion will increase the security of their users. Because, hey, everybody knows than writing your password in a text file or on a sticky note is much safer than letting Safari storing it in your encrypted keychain!
Maybe some people manage to remember douzens of randomly-chosen 12-character passwords. But the rest of use won't memorize more than a few passwords and think that disabling autocompletion is a considerable hassle. The autocomplete attribute is an horror which should have never been allowed to exist. Hopefully Safari extensions allow you to inject JavaScript into webpages so you can remove that attribute.
Delete That Damn Event is a Safari extension that forces autocompletion for all HTML inputs.
This project is provided under the Modified BSD License. You can read more about it in the LICENSE.md file.