We see this type of conversation happen from time to time. I appreciate mkroeker summing up the major points of the Content Policy thread and appreciate the insight from the other contributors.
The thing I would note is that our Content Policy specifically states that, when you upload, you are acknowledging that you are the rights holder of that design--whether through licensing, ownership of the copyright, agreements, etc.
Please do know that willful violation of our Content Policy may have legal consequences but it can also mean that your account is banned from our site. We try to be an open community and encourage designers in their creativity. Shapeways enables people to 3D print whatever they can imagine, which unfortunately occasionally includes things that already exist and may be covered by copyright.
While we do what we can to ensure the content on Shapeways is appropriate, we cannot realistically review every single model uploaded for a possible copyright infringement. We are also unable to determine whether the user has obtained a license for copyrighted content or are the original copyright holders in a dispute. As a service provider, our liability is protected by the Digital Millenium Copyright Act under their Safe Harbor provision. (More details can be found here on Wikipedia: en.wikipedia.org/wiki/Digital_Millennium_Copyright_Act)
What this means is that while Shapeways is protected by the DMCA, individual users, like yourself, are not protected and are thus liable for any penalties resulting from copyright infringement. We do not encourage infringing known copyrights and we are not legally able to provide specific advice on a case by case basis.
All that said, we are also a community that is about creation. In that, we ask that we all work together to encourage the type of community where sharing and creating does not violate trust and end in deception. When you willfully violate others' rights to their creations, it is not just a legal issue but an issue of violating the trust of our community.
We highly encourage you to not go down that path. We want your creative energy to add to our community, not to simply profit from it.