Unfortunately, many of the people who comment in this way are generally not open to any sort of meaningful dialogue. I suspect, as I wrote up top, that fear of change is a driver, along with an unwillingness to reduce or eliminate the foods we have grown to love.
I comment regardless and my response is almost always the same, "Educate yourself. Start reading ingredients. Eliminate processed food. Adopt a whole-food approach to living. Start incorporating plant-based dishes into your weekly menu. Try it all for a month. What's a month! Your body will thank you and the results will be well worth what may seem today as a sacrifice."