Do you have health problems anywhere in your family? A great way to "justify" it to people is to tell them that you are working hard to avoid the diseases inherent in your family tree. Sometimes people need a reason and don't want to hear the ethical "hippy" reasons. They would have to face changing their own diets if their heads were not in the sand and too many people want to eat now, worry later.
Tell your husband about the hormones in the meat and dairy industry, and the fact that it isn't good for your SON, who is a growing boy, to take in all those female hormones, specifically estrogens. Tell your husband you are protecting his prostate and tell him that it is the most prevalent cancer in all males and it is DIRECTLY linked to eating meat and dairy. If he resists then say fine, he can protect his own jewels but you are protecting your sons.
Tell your mom that it is absolutely for health reasons and ask her how she would have felt if her mother undermined her authority? Tell her that she will not be doing him any favors by clogging his arteries, which starts in childhood! Tell her and others that you respect their wishes and choices, please respect yours. The worst thing you can do is be preachy, or lay all the ethical reasons on them right away. A lot of people do not want to give up their fatty diets and will drag everyone right down with them (misery loves company) just so they can justify doing it to themselves.
Get indignant! Tell your husband you are doing this, it is important to you and the health of your family. Force feeding your son a fatty diet is cruel on his behalf if he insists on it. Tell him when your son is old enough to decide for himself, then he can, but as for his health now it is in your hands, and it is your job to be a responsible parent and keep him healthy. Tell your husband you will cook vegetarian and if he wants to eat something else he can go get take out or cook for himself, but you and your son are eating healthy, and you respect his right to eat what he wants for himself.
Be assertive and non preachy but don't let anyone give you crap for eating healthy, or feeding your son healthful foods.
