Are you suggesting that, in a conversation over the water cooler at an office about pets, it’s not appropriate to use the word “bitch” to refer to a female dog?
And the word “niggardly” is not an apt analogy. It’s an obscure archaic word that many people will not know, so there’s good reason on purely pragmatic grounds to avoid it to avoid the potential for misunderstanding.
The word “spade”, on the other hand, is a very common word for a digging implement. Unless you think that we should remove the word from the lexicon altogether for all purposes and use some other word for digging implements, why should its use to mean in a digging implement in one particular phrase be avoided?
In most cases that’s what’s going on, and I wholeheartedly agree.
But perhaps we should also be wary of real racists making use of innocuous phrases for the explicit disingenuous purpose of sneaking in racial slurs with plausible deniability.
I’m not Larry Borgia but I guess he had in mind this closing bit: ‘are you sure it’s spelled “Karon”?’ A suggestion that one does not know how to spell one’s own name would strike many as “assholish”, while “probably a little racist” likely derives from two of her three sons bearing black-sounding names, plus the Sade song title in her signature. Though the only “creatively” spelled name is her own, which she is presumably not responsible for.