To say a slope is "slippery" in a case like this says more about us than about the "slope." When a policy reaches the point of absurdity, we can recognize it and change the policy. The opposite view is that we have no judgment whatsoever.

And it *is* all a matter of judgment. If someone doesn't care about making a good part of their audience very uncomfortable (rather than a tiny handful) while encouraging bigotry (inadvertently, I assume), it really is their right. Likewise it's the right of others to suggest they do otherwise.

Moneylending was the business of some Jews. Nothing offensive about the fact. But to emphasize their Jewishness gratuitously in the song emphasizes their "otherness" from the singer and his or her audience, and reminds everyone that "Jewish moneylending" has been a big propaganda point for bigots for centuries.

While "The Merchant of Venice" indeed offends some people today, the fact remains that it's a more substantial work of art that's far more substantial than "The Waxies' Dargle," with plenty more in it to talk about, including just how we're supposed to interpret Shylock, who, unlike the moneylenders in the song, is a fully developed human being rather than a mere throwaway line.