We will have to agree to disagree on this topic. Saccharine has been around longer than any of the others and has been shown to be generally benign (you'd have to feed lab rats so much of it to make them ill that it doesn't reflect any consumption in the real world) but some of these other non-nutritive sweeteners (NNS) came along when some less savory chemicals were being invented.
The problem with many of the "generally assumed to be safe" chemicals and products is that while they test them in mammals, whether rats, rabbits, dogs, or humans, that research totally overlooks the gut flora that is impacted. Studies show that remote tribal populations living in non-westernised areas without processed food have a huge diversity in their gut flora; ours is greatly diminished. It's why Roundup (glyphosate) is so obnoxious - farmers literally drench their wheat fields with the stuff to kill the grain so it will dry on the stalk before it is harvested, but the residual chemical comes through our food. Artificial sweeteners are much the same way.
Don was cherry-picking with his formaldehyde remark, though his accuracy is under debate:
In the small intestine, digestive enzymes break aspartame down into methanol, phenylalanine, and aspartic acid. These metabolites are further broken down into formaldehyde and formic acid,19 each of which follows a natural metabolic pathway to be metabolized just as they would from other dietary sources.
I've skimmed quickly through this article, but it's one I plan to look at more carefully this weekend. They review the possible impact points of these NNS and look at studies and literature. A good starting point for more research.