One diet Snapple won't kill you, but some people do down liters of diet soda each day, and that is bad. As for whether it's worse to drink chemicals or worse to drink sugar syrup, well, there are a lot of different opinions out there. Both are bad, but it's not the end of the world if you do something bad now and then. So my suggestion would be to make Snapple (diet OR regular) a treat, not something you drink every day.