For clarification there are no studies that show that castor oil is harmful during pregnancy ( study shows not harmful, not helpful
). People have hypothesized it, however there have been no conclusive studies. And in the interest of real comparison, there ARE studies showing the danger of every other induction drug out there. The most severe documented side effects being fetal and maternal death. Coincidentally the side effects of medical induction meds are also passing meconium, fetal distress and dehydration (go figure). Castor oil has been used in the natural birth community, pretty much back to the use of herbs as medicine (ancient egypt) http://news.sciencemag.org/sciencenow/2012/05/just-a-spoonful-of-castor-oil.html
any artificial induction method is going to have some dangers, you are asking your body to do something it wasn't ready for. But when medically necessary they are great. Inductions shouldn't happen unless overdue or medically needed obviously. And the problem with castor oil is dumb-asses will take it WAY earlier than they should be inducing babies. So its difficult for it to be so easily accessible. But scientifically speaking there has been no correlation between castor oil and the passing of meconium during labor. Why does it have a bad rap? There is no proof as to why, but it would make sense though for the drug companies could feel a little threatened by something that could induce labor without as many dangerous side effects.