I think it's because in English-speaking places (I'll say "The US and some rounding errors" to be explicit) the fact is that for a long time, cancer was a death sentence. This led to anything that is hard to kill as being called cancerous and the avoidance of such things is important (yes, this is where you chuckle and mime smoking a cigarette. There's still a population of the US that believes "smoking causes cancer" is a conspiracy by Big Pharma to push more cancer treatments or some bullshit like that.)

Calling something "cancerous" is to say it was an incurable disease that unless stamped out with some amount of precision will continue to cause rot and decay. Be it correct or not, saying "The cancer that is killing HN" is pointing a finger at a problem and scapegoating all the other problems onto it.

Like how "going viral" is not really the negative connotation that one might expect?

Building part of an "emotional discussion" doesn't require the author to be experiencing particularly strong emotions as they write it.

Not that you have evidence of the author's state of mind?

I don't think the confusion you describe is happening.

That's a good distinction, and it pretty much captures the exchange. Both sides felt quite strongly; Helwig used strong words. But that doesn't mean either side was unreasonable, despite some of us commenters being discomforted.