OK, I'm not directing these comments at you two personally, we all get to make our own choices, but this thread is soliciting tips, so I wanted to provide my understanding of some of the context why someone might cringe at these things.
True margarine is full of trans-fats and has turned out to be far, far worse for people than the butter it was touted as a 'healthier' replacement for. Faced with choice between margarine or butter, my understanding is the consensus now is people would be better off using butter and as an alternative, there are olive oil sprays available.
Regarding artificial sweeteners, an uncannily similar process seems to be playing out. Initially promoted as a 'healthier' alternative to processed sugar, they are now, in study after study, being implicated in altering the microbiome of the human GI system to the overall detriment of the human.
And that's just the (mostly) physiological impact. Moving on to the psychological impact, these kind of swap-outs can be implicated in an issue some people manifest in which 'sacrificing' leads to overcompensation. A slightly exaggerated example is ordering large fries because one chose the diet soda.
As I think we all know, body composition management is an incredibly complicated subject. Each of us has to do our own due diligence and make informed choice about what is right and works for us. I like threads like this, where everyone can pitch in with what has worked for them so others can go through to see what fits for them. No one thing is going to work for everyone. I am loving IF, it just felt right and I took to it like fish to water, but I know there are many people for whom it feels insane and intolerable, so I could never pretend it's for everyone.