It’s “mathematically” correct but the extra “not” gets easily lost and is in a weird place. Plus it’s not specifically respectful to avoid the use of the word but rather it’s just common decency. In your sentence it puts more weight on the act of not saying it, as if using it is fairly normal and not using it takes some amount of effort.

It is usually better to use phrases like “it is considered disrespectful” over ones like “it is not considered respectful” even though they technically mean the same thing. The first is postively a bad thing and the second is negatively a particularly good thing, if that makes sense. Nuance is tricky business.