The Gemara (Gittin 55) relates that someone made a seudah, and accidentally his servant invited Bar Kamtza, instead of Kamtza. When the host noticed him dining at his celebration, he thought, "I wanted to invite Kamtza, my friend. I hate Bar Kamtza. I don't want him here."
The host asked Bar Kamtza to leave. Bar Kamtza pleaded to be allowed to stay. He even offered to pay him for the entire meal, but the host sent him out of the hall, and Bar Kamtza was very embarrassed. Bar Kamtza told the Roman king that the Jewish nation was rebelling against him. To prove it, he advised the king to send a cow to be used as a korban and to see whether the Jews accepted it.
Bar Kamtza blemished the animal, disqualifying it for a korban. The chachamim in the Beis HaMikdash wanted to sacrifice the king's korban despite the mum (blemish). They said that they should bring the korban for the sake of peace so that the king wouldn't be angry with them. But Reb Zecharyah ben Avkulas argued that they shouldn't sacrifice it because "people will think that a korban with a mum could be brought as a korban."
The chachamim came up with plan B: They would kill Bar Kamtza so he wouldn't be able to return and tell the Roman king that they didn't bring the korban. Once again, Reb Zecharyah advised against it. He explained, "People will think that whoever brings a korban with a mum is killed."
The chachamim accepted his views. The korban wasn’t sacrificed, and Bar Kamtza survived. He reported back to the king, resulting in the Churban Beis HaMikdash.
