Actually, Stevia is also widely used throughout other countries in Asia and also South America, being that it likes warmth and is easy to harvest.
Do you know how many plants out there affect fertility? And how many are Cyanogenic, or contain other toxins that are harmful in large amounts? Also, if a couple countries ban something that doesn't make it spawn of the devil - Raw Milk is illegal in almost all states in the US, as well as several other countries including in Europe, yet I'm still waiting on seeing someone die or get seriously ill from it.
Yes, I'm aware of the issues with Stevia, but there's issues with nearly every natural/plant based substance out there. . . The amount that is used is pretty miniscule anyway.
And I already mentioned, it's an acquired taste. Few people use it because of that, so, what's the huge worry? I don't use it much at all, (I just sample what I make for others) but I have a relative who does use it because she's diabetic.