“Large families who are on welfare are so because of the number of children they have.” What a thoughtless and cruel thing to say.
Really, paying rudeness for rudeness doesn’t ever help. People who say flippant comments don’t honestly know what they’re saying. This is why a simple response – similar to the third one, “I encourage you to reconsider” – is a very appropriate one. If it causes the stranger to pause and reflect, it will have made much more impact than an angry response.