It does seem like a weak reply to me - it's too equivocal. "We don't know" implies that it's anybody's guess, and that it should be avoided only out of an abund

It does seem like a weak reply to me - it's too equivocal. "We don't know" implies that it's anybody's guess, and that it should be avoided only out of an abundance of caution. Some people will interpret that response as "there's no evidence it's bad, so it's probably fine." In fact there's plenty of evidence it's bad, both direct (the linked study is not the only one) and indirect (we know that smoking in pregnancy is bad, and that drugs affect the fetus, and that fetuses are sensitive). If you polled medical professionals, they would all say it's probably bad. The likelihood that it's perfectly fine is small.