Why do people think artificial sweeteners (aspartame) is so bad?

Personal experience - I suffered from rashes on my hands for years and couldn't work out why. Then I saw an article in the newspaper about a woman who chewed large quantities of sugar-free gum and had a variety of symptoms that went away when she stopped chewing the gum (a doctor had suggested aspartame poisoning could be the cause). I stopped drinking diet drinks and voila, no rash. I know it could be psychosomatic, but I'm not planning on taking anything with artificial sweetener ever again.