Comment by sqeaky

No he wasn't. He was trying to disparage and insult a perceived threat. "Cancer" is an inflammatory and negative thing to call something no matter how you spin it.

Ballmer wasn't stupid he could have been nuanced and precise if he wanted, he certainly knew the difference between a kernel and a license. He wanted to convince people to not use a given technology stack because he was invested in another. If that is not convincing enough at the time there was already a more accurate but still negative sounding phrase "The GPL is Viral", but that wasn't offensive enough and didn't attack the perceived enemy OS.