To be fair, you had to look it up. It's possible if you didn't know it was in bad taste you'd have repeated it in the future as well.

> It's like pretending "that's all, folks!" doesn't immediately evoke Looney Tunes

It doesn't for people who haven't grown up with Looney Tunes. You're on a fairly international site here. Similarly, you can't expect everyone's education about the Holocaust to have covered this specific thing in a way they'd reliably remember and avoid an embarrassing mistake like that.

I'm Jewish and I didn't know what that phrase references, and I've also been to many Holocaust museums.

Yea but when I did, I couldn’t really find any reference to it devoid of Nazi association.

Since you needed to look it up, how about you give the author the benefit of the doubt rather than act so offended?

Now, if the quote had been "Arbeit macht frei" I would understand the outrage, but to me the English translation sounds more like a reflection of the Calvinist/Protestant work ethic from the time when the saying was minted, at least 100 years before the Nazis rose to power. To some people the quote in itself holds appeal, and why shouldn't it? If read without context it is actually quite inspiring.

Correct, you get to decide what the author meant and what his motivations were. It's not that he pulled an ambiguous, five word, phrase out of the back of his head. One which we've all heard and are all only vaguely familiar with. No, the author is actually a closeted racist. He chooses to push his racist agenda, not through directly communicating his ideas, but by using banal, dated, phrases which have a racist context which most people are not familiar with. It's really not possible to use these five, every-day, words in that sequence without summoning all of the racist intensity and hatred which some people attached to this sequence of words some time ago when most of us weren't alive.

You do not understand the distinction between insulting someone and offending someone.