Consider an AI chatbot platform. If this platform doesn’t allow users to create characters (that are stored on their centralized service) that infringe IP, but allows users to import character definition files that do so from external sites (that are created by community members, and may contain copyright-protected characters), without permanently storing (or storing for private use), is the owner responsible for IP infringement?
IANAL, but I’d say in your example: No. If you do it right. Other service also don’t need to be super strict with checking the copyright. You can put in stolen text into Office 365, have someone print you a t-shirt with the latest Disney character on it… I mean there are edge-cases and you better don’t admit your whole business is about helping people violate copyright… But I guess it’s generally alright to offer a service or tool that can be used to violate law.
And it might not even be violating IP. There are exemptions for personal use. I’m pretty sure I’m allowed to write (or generate) Harry Potter fanfiction for myself and my friends. So it’d be completely legal both for me and the service provider.