[DaiPlusPlus]

Right, but "slur" by itself is used as shorthand for "offensive slur" - typically racially-offensive slurs or homophobic slurs, and so on - I'm not aware of normal public discourse referring to everyday insults as "slurs" - whatever the original definition slur had it now has a connotation of insulting the target by way of comparing the target to an intentionally hurtful stereotype. (I could enumerate examples but nothing good can come from that, methinks...)

Whereas "TERF" is an acronym - it isn't appealing to anyone's emotional opinions about what a "TERF" represents - that is if anyone is even clued-up enough to know what it actually means.

Maybe the people complaining are assuming that TERF is an offensive slur without doing their research first? I'll admit it does have that feel to it, the way it sharply rolls off the tongue...

[kian]

TERF both manages to connote something that should be stepped upon and is used to box in a person's opinions to a caricature so that a label can be applied (a stereotype, in other words), rather than listening to what they say. I'd say that between that, karen, anti-vaxxer, and anti-masker, a number of niche slurs have been popularized recently.