Personally I use the following Mantra with most of the border line junk foods like Dite Rite (what I drink... same basic idea as Diet Coke, cept with splenda...)

"Everything in moderation, esply Moderation".

I perfer natural foods/products to chemicaly proccessed stuff, but we must not forget not everything natural is great for you either, and that there are some chemically made things that are as good as some of the natural, maybe even better depending on what item we are talking about.