So, it's ok for $BIG_EVIL_COMPANY to take open source code and use it at will, including uses that violate the license? If code cannot be owned, it cannot be protected either.

Note there's a clear analogue with books and movies. Stories cannot be owned. You are allowed to retell a story (there are only a handful of stories anyway, just a gazillion variations). But you cannot copy entire sections of a book, or use parts of someone elses movie in work you "create".