Just so we're clear: I think most parents are unreasonably afraid of chemistry sets. I agree with you on that. But --- bear with me here --- that's also a reason why we don't have to crack down on companies marketing chemistry sets.
As an aside, I don't see much effective difference between a legal crackdown and one caused by fixing the social context.
'Some degree of danger reduction' just doesn't qualify as a catch-all justification for regulatory action. At least not with me.
And in the magnet case, larger magnets are plenty fun while still being much safer.