Earlier quoted context omitted.
Many people consider 'dumb' more offensive to use as an epithet than than fuck is.
Why?
I understand that there's a whole world where swearwords are a big no-no, but half of them are jokingly used between adults: as long as people know when or how to use them non-threateningly, I don't think it's a big deal.
"Dumb", on the other hand, is almost never used jokingly, though it can sometimes be used in a self-depreciative way.