Scientists Make Part-Human Animals -- Good Idea?

Public money is being used to pay for research that create animals that are part human. From the MIT Technology Review story:

Braving a funding ban put in place by America's top health agency, some U.S. research centers are moving ahead with attempts to grow human tissue inside pigs and sheep with the goal of creating hearts, livers, or other organs needed for transplants.

The effort to incubate organs in farm animals is ethically charged because it involves adding human cells to animal embr...