I think the issue is that to remove the botnet, it requires having your code be executed on all infected machines. You can't possible get permission from the owners of the millions of infected machines to do this.
Yep. Imagine if it bugged out and broke all the infected machines. Even if the bug that broke the machines wasn't his fault, he'd probably still be in a grey area.
Even a bug that affects just 0.1% of a 1 million big bot net would still leave a 1000 unhappy users with broken setups that might consider themselves to have been better off with the bot net.
