[troyvit]

Nope I'm not implying that, but you certainly inferred it. Legality is one marker you can use when deciding ethics, especially in a democratic country. Also we're talking about the permissive side of the law (reselling used books), not the restrictive side (not being allowed to feed homeless people).

Maybe: "In some US cities it is literally legal to apply eminent domain to kick people out of their houses to enlarge a freeway" would be a better slippery slope, but that's still a totally different power dynamic.

So yeah I dunno. Try to come up with a better analogy, but definitely keep to your slippery slope. It'll convince somebody.