Of course, it isn't worth supporting for us, today, but at the times it thrived slavery turned to be the most viable form of labor, for that society.
Perhaps in future our society will evolve enough to make all software (and not only software) free. In particular, we should find a way to overcome tragedy of the commons.
> You can say the same thing about slavery, but that
> doesn't make it good, or worth supporting.
How, exactly, do you see slavery as having helped us progress as a society? Slavery held us back. Both literally and figuratively (we held ourselves back).
> But from an economic standpoint? It was a very
> effective way to accomplish a lot. As disgusting as it was.
As far as I can see, the only economic contribution was free labor. The presence of free labor makes the wealthy live very well while they are able to suppress resistance, but saying it somehow made us advance as a society - both in moral and physical terms - is the opposite of the truth, as far as I can see.
In ancient cultures they used slaves to build pyramids. I'm sure the ruling class told themselves that this was a symbol of how advanced they were - that they could build these huge things. I just see a colossal waste of time, with the only purpose being the ruling class having something to feel important about. Stacking rocks on top of each other is no more advantageous to a society than cheap cotton, at least not when the cheap cotton can't be purchased by those who need it the most: the people who produced it.
You can say the same thing about slavery, but that doesn't make it good, or worth supporting.