It's insulting to some perhaps due to their own self-perception but the definition of the word and its word origins are separate from how somebody feels about the way a word may have been co-opted over a period of time. Retard is interesting because its meaning is pretty clear and innocuous. The word is also quite useful.
If you say a material is fire retardant, you not only are free to say this, it would be ridiculous to have to invent or supplant a new word because one was co-opted over time and personified, turned into a noun. People will disagree, but it takes mental gymnastics to be offended by things like that.
That's why people have developed the SJW social justice warrior moniker and I think it fits well. Because it's an imaginary problem and working within that framework these kinds of people will eat themselves to death. So why engage or contribute to it at the expense of time, logic, and a reduction in cohesion of everyone else working towards goals.
You have to give people the power to use words like this where a true meaning well defined is absent of insult and if used as insult, if not specifically directed at someone, you can't allow another person's claim of offense to affect the conversation thats apart from them.
this is my biggest problem of a lot of the narrative spread by certain people and the media. maybe it's a thing with modern society where foolish people misidentify real problems and instead use their valuable time on things like microaggressions thereby taking focus (sometimes on purpose) off actual aggressions. And so far it's recipe for a failed state. Christopher Hitchens said it well. "The fact that you’re offended has absolutely no bearing on the truth of the matter"
The sad thing, the very sad thing is the media do better on these kinds of controversies because they generate views. I have chosen to participate here on this in hopes it might actually set somebody straight. The people who claim this kind of censorship are the same people who purport that there is strength in diversity. But unfortunately they don't really know what diversity really looks like in terms of diversity of ideas. They imagine it means comfort but they are wrong. Understanding diversity means bearing with discomfort and dealing with the imperfections of speech, perception and letting go of this idea that you can break down useful frameworks and infrastructure and it will make things better. That's not how one becomes a valuable participant in anything and they make communities suffer.