Talking about "thieves" is very much going back to the idea that software is the same thing as physical things. When talking about software we have a very simple concept to guide us: the license.

The license of html5ever is MIT, meaning the original authors are OK that people do whatever they want with it. I've retained that license and given them acknowledgement (not required by the license) in the README. Simon has done the same, kept the license and given acknowledgement (not required) to me.

We're all good to go.