-How can Linux be maintained in such a way that it never gets distributed with code that belongs to someone? I’m not totally familiar with the way open-source works, but certainly it isn’t right to use someone else’s code and distribute it for free if the origional creator didn't want it used that way.

By use of legal reverse engineering techniques. Imagine a double ring of trusted people around Linus. The outer ring receives untrusted patches and writes down a formal description which is then passed to the inner ring of implementors who work for companies that put down in writing that their employee's works can be released under the GPL. That way only the ideas are carried over.

Ofcourse with the broken US patent system where basic algorithms can be patented this only avoids potential copyright infringements, not patent issues.