You bring up a valuable point, and I agree with you - the mere fact that a meal is home-cooked does not guarantee its being healthy. One has to know how to choose the best ingredients of what is available, balancing between optimum health, taste and economy, and to use healthy cooking methods. That is why nutrition and wise consumerism are two subjects which are so useful for a homemaker to learn.
Having said that, however, I will maintain that it is easier to produce healthy meals at home than to obtain them elsewhere. Most commercially prepared foods are a poor choice, because food manufacturers think mainly about profit, not health, and thus use the cheapest ingredients available.
The phenomenon of leaving frozen pizza and instant soups for children to have for lunch after school, too, is rooted in the absence of someone to welcome them home. Of course, it ispossible to work full-time and still leave a wholesome meal for the children to have after school, but the fact remains that too many children have substandard fare as their main, and sometimes only, hot meal of the day. Some are picky eaters; even if there is "real" food in the house, they will not be induced to eat it alone, without anyone to serve them and keep them company.
And, of course, sometimes the simplest choices are the healthiest ones. It is easier to prepare a fruit platter than to bake a cake, and arranged in an attractive way, it can be an excellent dessert. I personally love an arrangement of kiwi and banana slices, with some strawberries on top. In the summer we have chilled watermelon for dessert quite often, which is very refreshing. And on Shabbat nights we often skip dessert altogether, because everyone is so full.
Just a word about fats: after reading "Nourishing Traditions", I was confirmed in my earlier suspicion that it is the quality, not quantity of fat in our diet that matters. We have been using butter, cream, cheese and so forth in our diet more liberally than before for the past two years, and none of us (well, except for the children, of course!) gained an ounce of weight.
I really, truly believe that real food, made of good-quality natural ingredients, even if it is rich (and our ancestors in the not-so-distant past ate a diet which contained much more fat than what modern nutritionists are trying to get us to eat! My grandma still smacks her lips when she tells of goose fat spread on a warm piece of challah), does not by itself cause obesity, if it is eaten moderately, at a cheerful family table.