Answer:
The third sentence - "It is upsetting to think that society punished these people who are now considered heroes".
Step-by-step explanation:
The given statements except for the third one, are depicted in an informative tone that displays and describes the readers about the sacrifices made by Martin Luther King Jr. and Nelson Mandela for the reformation of society. The third sentence is going off track as it portrays the consequence that they faced which is diverting the tone and flow of the information. Thus, this one is off-topic as the focus here is not towards the brutality these heroes faced but the sacrifices they made for their beliefs in order to reform the society and how eventually they became successful in their attempt.