Not defending your friend, but I think part of it is the association with highly processed foods.

I developed a soy allergy, and I was shocked to learn how much it’s restricted my diet. In two years I’ve found one brand of hot dog buns I can eat. If you you look at almost any fast food restaurants allergen menu you will see soy in almost every single items contains soy. Mayo is a effectively whipped soybean oil.

I don’t think it’s a conspiracy, but it’s a cheap additive and seems to have some preservative quality, and a good indication that you’re food is highly processed. I eat much healthier now, largely against my will.