@Vicki C My understanding is that the safety concerns relate primarily to the uncured silicone, i.e., when it is soft and sticky out of the tube. Once it is cured, the skin toxicity is supposedly minimal. After all, in the USA at least, we all have caulking around our water fixtures, shower walls, toilets, baseboards, windows, and doors.
That being said, I hadn't thought about the possibility that chemicals could leach out even from the cured silicone into the soap. Given the high pH of the soap batter, that's entirely possible. I'll see if I can find anything further about that from a reputable source.