Here's my take on this. If you want want to be a vegan who eats only natural, organic, non-GMO produce, go ahead. More power to you. However, just be appreciative that you live in a country where you have that choice.
There have been concerted efforts by environmental organizations to push organic and non-GMO farming on the developed world. To put it bluntly, it is paternalistic, racist, and it's killing people. Then there are people like Norman Borlaug, who few have ever heard of. The man who saved a billion lives by introducing high yield GMO plants to third world countries. The fact that Monsanto owns and is very protective of patents on GMO seeds is a big issue, but not a science one. People need to stop confusing the two.
As for artificial sweeteners, I think the debate is still out on that. There's been a lot of controversy over aspartame but no conclusive research. Over 100 regulatory committees have deemed it safe. Saccharin, the original artificial sweetener was known to cause cancer in lab rats. Any diet product probably isn't good for you. I think a lot of the weight gain commonly associated with diet soda probably is more psychological. Junk food consumption of any sort should be in moderation. Pop isn't meant to be a replacement for water, nor sweets a replacement for food.
For starters, even our experts can be wrong on what is safe. It's happened many times in the past, when for decades something was considered perfectly safe and then they found some new scientific knowledge, and they turned around and went, "oh shit, sorry folks, this is actually terrible for you. please stop consuming it immediately."
That said, I have no opinion on GMO and, in my belief, the jury is still out on that one. I don't seek it out, nor do I avoid it... I just don't care if I eat it or not. If I buy something that is, whatever.
Artificial sweeteners, however, are a mixed bag. Some still have documented possibility negative health impacts, but I believe some of the issue may have been bad studies. I don't know about that, but I avoid most artificial sweeteners out of principal. The principal being, I prefer naturally-available chemicals as opposed to lab-generated, if at all possible. Even if it's a lab-generated version of what can be found in nature, that's cool. I don't think Ace K has ever been found in nature, nor has Aspartame or Sucralose.
In my eyes, the truly worst aspect of those three: they do nothing about blood sugar. If you have a diet designed to limit sugar intake for whatever reason, be it because you want to lose weight/cut fat, have an insulin problem, etc... those three chemicals cause a reaction in the body that essentially creates the same spikes in glucose and insulin levels, because the body THINKS it is getting sugar.
Sugar alcohols do not exhibit that issue, and better yet, neither does Stevia.
Whenever I'm looking to buy food I've bought before, I aim to buy the type with the lowest true sugar content. I also aim to avoid products full of artificial sweeteners - Stevia has been slow to rise but there are more products using it these days.