Trying using a CA compliant gas can to fill up your CA compliant riding mower then put said mower in reverse and back it out of wherever it's parked. For bonus points do so without a helper. Stickers and warnings are one thing. Mandating consumer safety features can go wrong easily.

In some areas "this product not for sale in CA" is a marketable feature. On small engines it means it's tuned to run well instead of minimum emissions. For gas cans it means you don't need three hands to pour from them. For riding mowers it means you don't need to go out of your way to engage several redundant safety mechanisms in order to operate it (In addition to reasonable safeties like a seat switch and shifter that can't easily be bumped).

I can't think of one off the top of my head but I'm sure there's equally "pants on head" consumer safety laws about things other than garden/lawn equipment and/or in states/countries other than CA.

(BTW, this is post is the cliff notes of a conversation I had with my coworkers at a tech company so it's not like we're a bunch of hicks complaining that the guards on our saws prevent us from fitting oversized blades.)

Is it such a bad thing to value reduce emissions from some of the worst forms of easily avoidable pollution, i.e. spilled gas and two stoke engines?

If you were around when the air quality in LA was almost as bad as what we are seeing now in places like Beijing, you might agree with some of the provisions that were enacted (and were hugely successful at reducing pollution not only in CA, but elsewhere due to said "features".)

Man, I hate those gas cans. I've used a bunch of different cans with "safety" nozzles, and every time I get gas on the equipment, the can, the ground, my hands, etc. They're much worse than what we had before.