There is no reason to avoid sugars, just limit them.
If the diets use AS a lot, it's because they recognise that people will want the sweet foods and can't do without it. So if you're going to eat sweet things, it's going to be far less carbs to have an AS than real sugar. So that's why they use them.
Stevia is a natural sweetener so you could look for foods with that.
Other than that, should YOU use AS or smaller portions of real sugar? That's up to YOU. There's no health/diet reason at all that either is "better". As stated, eliminating sugary treats entirely is the best option, but if you're going to have some, whether you have very small doses of real sugar, or larger portions of artificially sweetened items, doesn't matter. Just as long as you're not cramming your diet with sweetened foods all day!
Whether it's AS or small 'real' portions, if it fits in your macronutrient ranges and you feel okay doing it, it's fine.
Deb, in New Zealand