|Serious Eats' 3 Ingredient Stovetop Mac & Cheese|
Sometimes their beliefs stem from personal experiences and experiments. Other times they come from one or more family members who have complained about a particular dish (rather than be thankful that someone took the time to cook for them).
I can also tell you that many of the folks who don't cook regularly believe that if they were to start doing so, they'd need to be cooking "healthy" foods.
Why sure, cooking especially healthy meals is a nice aspiration, but if you're a beginner in the kitchen, why not instead focus on cooking meals that while perhaps not incredibly healthy, are meals that you're confident that you or your family will enjoy?
The goal really is to gain comfort in the kitchen and/or to gain the trust of your family members that you can cook yummy things.
So if you're a beginner in the kitchen, maybe cutting your cooking teeth on less healthy meals will encourage you to gain the skills and comfort you'll need to slowly improve your repertoire, and in so doing make the kitchen a room in which you actually enjoy spending time.