This particular woman, who is not a health professional of any sort, made the claim that artificial sweeteners cause retinopathy and neurophathy. Retinopathy is a disease of your eye that can cause blindness and neuropathy is a disease of your nerves that can cause either pain or loss of feeling. She said that these diseases are common among diabetics, so it's no coincidence that diabetics have these problems since they often use artificial sweeteners!
The problem with her statement is that she doesn't understand what causes these diseases in diabetics. Retinopathy, Neuropathy, and Nephropathy (kidney disease) are caused by the osmotic load uncontrolled diabetes places on your organs. God designed our bodies amazingly... they can be so flexible and undergo a LOT of wear and tear... and yet there's a point when the stresses on organs is just too much. When diabetics have uncontrolled sugar in their blood for long, extended periods of time (like >15 years), it wreaks havoc. It changes the makeup of body fluids and pulls water and proteins in and out of places it usually wouldn't. Although that's a really simplistic explanation, it is essentially what causes eye, nerve, and kidney disease in diabetics. There is TONS of supporting research that shows diabetics who keep a very tight range of blood glucose DON'T DEVELOP THESE PROBLEMS.
I'm certainly not saying all sugar-free products are the answer or that we have all the research we need on them to confirm they are safe in all amounts of consumption. But I will encourage you to be careful what you believe. Listen to your body, follow your convictions, but be wise and discerning who you accept food information from. (And if you're still worried, go ahead and switch to Agave or Stevia!)