"This is a good question with a whole myriad of
possible answers. Terry suggested:
""If you ask most developers, they'll say they want a copyleft,
because they want to avoid their work being co-opted or exploited
(or even "hijacked")."
While this was a reason, it's not the main reason I chose
copyleft. It's not even something I directly considered when making
my choice but it was a "bonus" side effect if you like."