Why did Cato think that Carthage must be destroyed?

Context: Although Rome was successful in the first two Punic Wars, as it vied for dominance with the seafaring Punic city-state of Carthage in North Africa, it suffered a number of humiliations and damaging reverses in the course of these engagements, especially at the Battle of Cannae in 216 BC. Rome nonetheless managed to win the Second Punic War thanks to Scipio Africanus in 201 BC. After its defeat, Carthage ceased to be a threat to Rome and was reduced to a small territory that was equivalent to what is now northeastern Tunisia.

However, Cato the Censor visited Carthage in 152 BC as a member of a senatorial embassy, which was sent to arbitrate a conflict between the Punic city and Massinissa, the king of Numidia. Cato, a veteran of the Second Punic War, was shocked by Carthage's wealth, which he considered dangerous for Rome. He then relentlessly called for its destruction and ended all of his speeches with the phrase, even when the debate was on a completely different matter. The Senate refused to follow him though, especially Publius Cornelius Scipio Nasica Corculum, the son-in-law of Scipio Africanus and the most influential senator. Corculum opposed the war to preserve Roman unity and argued that the fear of a common enemy was necessary to keep the people in check. Like Cato, he ended all his speeches with the same phrase, "Carthage must be saved".

Answer: Cato felt that Carthage had bounced back too quickly from its defeats in the first two Punic wars, and would have remembered the disastrous defeat at Cannae. He thought that only completely destroying Carthage would remove it as a threat to Rome.