Horses are able to provide more than muscle power! They can tread over ground unsuited to the most primitive vehicles. They can fit in narrow spaces, they don't require petroleum, and they have enough intelligence to avoid certain kinds of absentminded user error. They are animals and they have personalities that machines will never have.
Surely someone could find new uses for old horses, after all they are organic and adaptable in a way that machines aren't.
And somebody did find new jobs for those horses! 2% of them, at least. The balance got slaughtered.
You can wave your hands and argue that the jobs are out there or will appear given sufficient creativity, but the market simply doesn't care about the faith you have placed in it. Your optimism doesn't control the unemployment level. We have to prepare for the eventuality that the jobs don't materialize, and we have to do it in a way that doesn't heap perverse incentives onto the unemployed while choking off the very consumption that fuels the economy in the first place.
"And somebody did find new jobs for those horses! 2% of them, at least. The balance got slaughtered."
I do not think this was as much of a slaughterhouse as that makes it look. Today, horses typically live for 20-30 years or so. In 1900, I would think working horses would be lucky to reach 20 years; as they became older and less productive, they would be sold of and slaughtered.
With an average 'working career' of 10-15 years or a horse, just stopping buying replacement horses would be enough for most of that decline in the number of working horses.
No. Just look at the horsemeat scandal. Large numbers of horses were being slaughtered in Romania and Ireland for economic reasons and are being eaten. They cost a lot to feed.
Humans can do so many, many things that if one is undervalued, they will look at others.
Some maybe we should stop saying that we are factory workers and must stay factory workers -- it just doesn't work that way, and truly never has.