lol, these two statement contradict with each other.
If there is a debate about weed while pregnant, then, the statement weed won't ruin your body is completely false.
Earlier last century, it was inconceivable to think that smoking is harmful to the body. In fact, they promoted smoking as healthy to the body.
Also, concerning illegal drugs, if you worry about the law, don't do it.
Some jobs/professions won't accept you if you broke an illegal substance law.
"They didn't think so back then!" argument doesn't really work here considering how much science and medicine has advanced since then. There are people all over the globe who smoke pot, many first world countries have pot legalized. These people have been studied a lot, and if there were any serious adverse effects of smoking weed, we'd know about them already.