[suvelx]

But if I can enter stuff into the blockchain (And presumably I can, you can't breed pigs by consensus...), why would i care about double-spend?

If I acquire some stolen pigs, or some pigs from a less than ideal lineage, I'll just enter them into the blockchain and say they're the result of breeding.

Blockchain works because it's verifiable. Breeding pigs, digging carbon (in its many forms) out of the ground, turning these things into other things isn't.

[taneq]

I'd presume that entering them into this blockchain would require submitting their biometrics, at which point it'd be indelibly recorded that you had 37 new pigs, 33 of which looked identical to pigs stolen last weekend. Or you could fabricate biometrics, at which point you're fine until you try to sell them and then someone notices that the pigs you have aren't the pigs you own in the system.

[jacobush]

It also makes it harder to keep, say, 2000 untaxed pigs, plus the 1000 pigs you pay tax for. Then sell the untaxed as one of the 1000 official pigs, but each official pig gets sold 3 times, each to 3 slaughter houses. If everything is publicly recorded, such as on a blockchain, you can't get away with that as easily.