> there is no legitimate reason for preemption to apply to labeling laws (even as broken as California's labeling law is), as labeling a product a certain way is not a mutually-exclusive action.

That's not really what preemption is about. A major point of having "interstate commerce" -- actual products crossing state lines -- at the federal level, is to prevent states from enacting trade barriers.

Suppose California disproportionately has more organic food producers and other states make higher proportions of food products grown with glyphosate. California then passes a law requiring the latter (i.e. disproportionately out-of-state) products to carry a scary warning label based on inconclusive evidence. Are they trying to enact a trade barrier? It sure looks like one. Meanwhile if the stuff is actually dangerous then it's dangerous in all 50 states, so the warning label should either be everywhere or nowhere according to the evidence, right?

Relatedly, having dozens or (at the city level) hundreds of different sets of rules is also a kind of trade barrier. Some small business in Ohio is willing to ship nationwide but every state has different rules, they might be inclined to cut off everyone who isn't in the local area since that's where they get most of their current sales, but that's bad. So then there is a legitimate interest in being able to say the rules have to be uniform if the states start trying to micromanage too much.

The better way to do this would be to only apply the interstate commerce rules to actual interstate commerce. So they could preempt California from requiring labeling on products shipped from Ohio, or require specific federal labeling on the things that are, but only California gets to decide about the things that never leave California. A lot of states would then say you have to follow the federal interstate rules even if you don't cross state lines, but it would be their decision and some might not.