There's an argument (and while I an pretty up on IP law in the United States, I am not a lawyer, etc. etc.) that, by providing code via an open-source license, you're handing anyone who uses it a defense (again IANAL but I believe the magic word is "estoppel" here) with regards to suing them for acts downstream of using it. In normal-person terms, it'd be along the lines of "you used an open-source license intended to permit, if not incentivize, the use of this thing; the only reasonable way anyone could use it is by violating your IP; therefore, you are implicitly granting permission to use it regardless of the status of your IP."
This has not AFAIK been tested in any court, but (to my mind) it's not an unreasonable point to accept.
CC0 actively does not provide any protections with regards to patents, which would make the above defense inapplicable.
> Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use …
It would be interesting to argue that, yes, I gave you the right to “use” this software but you actually had to pay me extra for a patent license.
