"Fetal farming" refers to the use of fetal tissue obtained from a pregnancy initiated for research purposes.
Many people think that fetal farming doesn't actually exist, and there is no evidence that proves it has ever happened. So they are banning something that they just made up. If they can do that, then I want to ban research on people who live in the 5th dimension. Poor Mr. Mxyzptlk has been through enough.
Where fetal farming comes from, I think, is the land of slippery slopes where a lot of right-wing conservatives live. It probably comes from the same place where people think allowing a gay couple in a loving, committed relationship to marry will lead to people marrying goats and kicking puppies (or something).