Sorry I'm Not Sorry - I gotta rant!

I suspect the first person [with a hypothetical fast-food-based diet] wouldn't be satisfied or feel as good as possible and thus would change his or her diet naturally, based on what works. I just don't think it's sensible (or morally right) to lie and tell that person he or she cannot lose weight unless fast food is excluded.

Now, if that person says he or she is hungry and asks for advice, I'd point to food choice (and have seen that happen here). If the person asks about nutrition or the like, same. But I've also known someone who lost a bunch of weight and ended up changing her diet to be much healthier by first starting by reducing fast food portions and paying attention to calories. Sometimes it's a process, and sometimes a really long one...

Depends who you ask. A shocking number of people claim to be "clean eaters" and eat lots of processed foods, and plenty of others claim that "clean" means no white foods or grains or sugar or any number of other self-defined rules.

Given this, I think we should all just acknowledge that "clean" means nothing in particular and is mostly just a way of claiming that the way you eat is superior to the way someone else eats.

Personally, I think about what I eat, but some of it--like yogurt, cottage cheese, smoked salmon, probably frozen veggies and canned tomatoes in the winter, steel cut oats, whole wheat pasta, quinoa, protein powder, etc.--is processed. Rather than thinking of these things as "cheats" or "unclean" (weird), I consider them to be foods I have chosen to eat because they meet some nutritional or taste consideration that I find important. Along with that, I'd include ice cream (homemade or otherwise), the pie I will make on Thanksgiving from fabulous ingredients, and the meals I get from restaurants, whether lunch places that meet my nutritional requirements and quality concerns or the various local restaurants I like for the occasional dinner....

On cheat days (since the OP apparently likes to think of herself as a "clean eater" who "cheats"): I don't cheat. I am concerned about overall balance and nutrition. I don't see why my diet is less healthy if I eat a 45 calorie Café Tasse Noir (my current favorite bit of chocolate to have after lunch on occasion) or even 200 calories of ice cream if I have lots of calories and have had my protein, fiber, and veggies. Re chemicals and additives, there are various things I choose not to eat (I don't personally choose to have HFCS or added transfats, and I simply don't like most packaged foods when compared to what I can cook myself), but I think a blanket prohibition on "processed" foods is too broad. There are many processed foods (the ones listed above, legumes, which I should eat more of) that are nutritionally positive. A focus on simply excluding allegedly bad foods and not creating a sensible balanced diet that meets nutritional needs and tastes good seems to me the wrong focus.

IME, if you focus on the sensible balanced diet, you aren't even going to want to or have room to be immoderate wrt high calorie sweets or chips or whatever it is that you are concerned about, other than rarely. I have a weakness for French fries, personally, and yet I did not need to cut them out or some foolish thing that would cause me to think about them more, and certainly not to declare them "unclean" (which makes no sense, especially since I can make them myself out of nice, clean potatoes). But because I'm focusing on other things I don't eat them often at all. And when I do I enjoy them and do not feel guilty or beat myself up or think I've polluted my body or fallen off the wagon or whatever. Ugh.

I think that people just need to find what works for them. I prefer a balanced diet that includes treats. I do not need to eat 100% clean in order to lose weight. I think people are mixing up goals...

If your goal is to lose weight, eat at a deficit.
If your goal is to retain as much muscle as possible while losing weight, eat enough protein and find a progressive resistance training program (e. g. Starting strength or StrongLifts).
If your goal is to be overall healthy (feeling good most of the time and having good blood work, etc), maintain a healthy weight, get enough rest (sleep and non-exercise days), drink enough water, eat enough fat, get your micronutrients, and maybe do some form of cardio.
If your goal is to stay sane, don't give up foods you love. Try to work them in or take a temporary break from them until you can show some self control.

Lol.

You are a brave, brave soul. I don't have nearly enough time to go into everything I think on this subject, but I'll throw in these two cents:

I work in the biomedical research field (cancer). About two months ago, the director of the NIH came to my university to give a talk about many many things. Among the data he presented was the risk factors for various types of cancer. Everyone knows smoking is number one for lung cancer; the number two risk for colorectal cancer was processed meat (and the risk of cancer increased with any amount of processed meat consumed).