@acoder re. your guinea pigs for food idea: Have you ever raised, slaughtered and then eaten an animal?

And, looking at the subject from another angle: animals are certainly not low-maintenance, you should be prepared to check on them at least once a day, possibly more often and there will be additional costs, e.g. for vet visits. Mowing the grass once or a few times by hand is significantly less effort.

Example: during lamb season we spend on average three hours per day with our sheep, if anything goes wrong, even more. Not to mention what happens if we have to bottle-feed some - think newborn baby.