I don't mean to be ignorant, but isn't it dangerous to assume offense in rote?
I am certainly not the first to inform you that "Git" is a slur in Britain, but we all commonly use a software for which it is named.
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If I were to argue in defense of "Spanish Flu" in particular, it's because of two major factors:
1) Education is good enough that people do not associate it with spanish people, in fact "flu" is not a dirty disease either, other exonyms from the period were "the Russian Pest" (IE: pestis) which are of course inferring some level of uncleanliness.
2) Everyone knows the Spanish Flu killed millions, but they do not consider it the same as influenza. If you say "killed more than influenza" it does not invoke the desired idea in the reader.
Thus, controlling the speech limits our ability to effectively reason about such a pandemic. Influenza as it is known today is not the same as the Spanish Flu, there is some distinction that needs to be made.