the issue is that we have really hard-hitting evidence on sugar being bad for us and causing weight gain. meanwhile, artificial sweeteners have been around since the 1800's and are thoroughly studied, yet the majority of research on them shows most of them are safe with the exceptions being saccharin and possibly sucralose.
it also has thermodynamics on its side because they are 0 calorie.
I'd like to note that I do not fully disagree with everything you've said in this thread but there are some parts that are odd.
as an example. you are against artificial sweeteners but Erythritol is heavily studied and you can bake with it. so why not advocate to replace sugar with it in things like cookies if someone has a sweet tooth?
you should also point out what it is about processing that makes a food unhealthy for consumption. the act of slicing an apple is processing it. if you tell the people you train that they should be scared of processed food and don't explain the types of processing that are bad, then they will just be scared of food when the overall goal of a diet should be sustainability and calorie restriction.
on the topic of clean eating. If I mix protein powder, flour, baking soda, stevia and cocoa together I can make cake. I can eat cake every day at every meal and still be "eating clean" according to the foods you listed. So you should start by telling people what the goal of a diet should be first is important.
also, the foods you listed as clean foods, most of them are processed and not eaten by "clean eating" communities like flour of any kind and dairy. Flour and dairy products are often much more processed than most snacks that you would probably condemn.
cheese, for example, is heavily processed. whey is also a by-product of cheese manufacturing which is then processed to make protein powder. There's also more studies showing shady manufacturing processes with whey protein than there are against the processing of artificial sweeteners. A few big studies done showed most protein companies have trace amounts of metals/lead in their powders.
and I say all of this as a non-clean eater.