You're right that it does contradict itself, but the unfortunate situation is that public domain declarations don't work and would make it harder for people to use your code safely in the current licensing model. The closest options are Unlicense and CC0 afaict and both don't work in many European jurisdictions.

I just want people to be able to take my code and do whatever the hell they want with it (including commercially) and optionally contribute to it. Having a license currently makes that easier but every time the Free Software lot going zooming off into the weeds of GPL v3 versus GPL v2 versus LGPL my eyes roll back into my head and I internally start screaming "get a life!".