The term has been removed from most recent medical literature, because the use of it has been inseparably tied with mental disability. You can't exactly justify calling a black man the n-word because he is a criminal, no?

Trying to find situations where it's "okay" to use slurs as insults is creating a loophole based on opinion that will broaden with time, implying that there are individuals who "deserve" to be called slurs and those who don't. It's creating a divide that can be easily exploited. It's best just to find another word.

The only appropriate use I know of is when talking about flame retardants. The word inherently means "to slow down/reduce", so using it to describe people inherently classifies them as "slow", another common insult term for mentally disabled people. Using it towards fire is a direct use of its wording and doesn't have the same risks.

Basically, the damage is done and the association is there, and it can't really be removed simply because the slur is used "accurately", you know? It carries the harmful context with it.