First, you must understand some basics. SHTF situations, are not only plausible, but have a degree of likelihood. Hurricane Katrina, LA riots, etc. So there is logic in being prepared. Since there is logic in being prepared, then those who belittle being prepared are not thinking logically. Instead, they are thinking emotionally.
Human children are known for letting their emotions get the better of them. Sadly, many grown women (and gamma males) have often faced no real consequences in life for their actions, and thusly fall into this category, as well. So, if someone is reacting emotionally (ridiculing your preparations), then the only logical means of handling the situation is to resort to treating that person as the child they are.
If you are new to this type of response, then please, dear reader, Google it. One of the best methods of dealing with children and those ruled by emotion over logic.
Agree & Amplify
This is primarily a method for dealing with shit-tests. However, when dealing with a grown person behaving emotionally, then it becomes a good tool to use. Agree with their statements and amplify them to ridiculous proportions. Best used in situations where looking like a jerk won't harm other interactions.
Dismiss & Ignore
Works in 1-on-1 situations. This might be your best defense. Also known as walking away. The implication here is that the other party's statement is so asinine, that they can no longer be taken as being serious nor credible.
Ridicule & Reframe
This might be a better option in social gathering scenarios than Agree & Amplify. Keep it short, and factual. Remember, people don't win arguments with long drawn out explanations. Arguments are won with zingers:
"So you don't think there will ever be another LA riot or Hurricane Katrina?!?! Let me guess, nothing bad ever happens in your world. I bet you don't even keep a fire extinguisher at your house either! Glad I'm not your insurance agent!!!"