I think rhetorical devices as a means of conveying sentiment is not only reasonable, but an essential part of the English language. I know, as does everyone else, that deeming someone to be a "cancer", is common accepted use of the term.
What I also know, is that individuals who believe it is reasonable to threaten violence over their own irrational feelings about common vernacular are useless, and their behavior should be shunned.
Grow up, snowflake.