Why not?
People still use "nigger" as a slur.
And especially why not for those who used it before the Nazis desecrated it?
Just to be clear, it's "nigga," not "nigger" and if anyone not black started throwing it around (well, a lot of black people don't even approve of their own using it) it wouldn't be seen as cool. My parents use it. I don't. It feels wrong. I feel like hitting those dumbass white kids who throw it around like they're wannabe gangsters.
The word isn't any more rehabilitated or reclaimed than "chink," "kike," "wet back," or "cunt." Just because the group that the insult is designated for uses it, doesn't mean it's reclaimed and rehabilitated. My Mexican friends might joke around and call themselves beaners, but I don't jump in with them.
As for whether or not you should use the swastika for it's original use, well, I don't care. As long as you're aware that there are those who still have negative feelings attached to the symbol, and you don't act outraged when they express said feelings. And pretty much this, too:
I would assume that someone using the swastika as a religious symbol would be wearing it 'in context' with religious regalia or as a design element, and not as a giant red-and-black icon on a t-shirt.
If I saw someone wearing a swastika on a t-shirt, I wouldn't step closer to see that it's made of little words, or that there's fine print explaining that it's being used in some other context. I'd just think "Scum", avert my eyes, and walk quickly away. I wouldn't ask for an explanation, any more than I'd ask a guy with a banner exactly what he means by 'Neo-Nazi'.
Pretty much my thoughts. Cultural appropriation sucks, but it happens. Until WWII is a thing of the past, I'd see it as pretty insensitive to use it as a logo, or a public spiritual marker where thousands of Jews might be present because intent simply does not matter.
In a way, I'd almost say it's like Zwarte Piet. Almost. Not quite.
I suppose I simply don't know what's the big deal is about reclaiming symbols and words. As a black female, I have no interest in reclaiming "nigger," "bitch," "cunt," "slut," etcetera, let alone words that offend other groups, regardless of their previous meanings. Words evolve, but if we're even having this discussion, they probably haven't evolved enough.