Final answer:
The best counterexample to the theme of heroism in disasters is the excerpt where it is stated that individuals showed panic and self-interest, contradicting the belief that disasters bring out the best in people.
Step-by-step explanation:
The excerpt that best provides a counterexample to the theme that disasters can cause everyday people to do heroic things is: "Contrary to the belief that disasters bring out the best in people, this incident revealed a darker side, where individuals succumbed to panic and self-interest." This statement directly opposes the common perspective that challenging times and disasters lead to displays of heroism by ordinary people, instead highlighting the negative reactions such as panic and selfish behaviors.