There's no downside. Thank God someone thought to make it non-toxic. Blame the smell. You pry off the lid of Play-Doh, and that sweet, unidentifiable aroma wafts out. It almost smells like a number of things, many of them yummy.
Some people think it smells a little bit like vanilla.
Kids being what they are, that's a green light to drop a ball down the gullet. As an adult, you have to wonder why salt is an ingredient in the stuff. I think the salt is there specifically to keep kids from eating an entire can of the stuff. Kids will eat anything, but they prefer that anything to be sweet. Salty obsessions come in those teen years.