The Second Beit HaMikdash was destroyed because of sinat chinum (baseless hatred). The gemara argues that we must understand the evil of sinat chinum to be equal to the combined evil of the three cardinal sins (idolatry, incest/adultery and murder). Since our exile is still ongoing, and the Beit Hamikdsh hasn’t been rebuilt, we know that we haven’t fixed that sin. We must know that Lashon Hara and embarrassing someone is compared to murder. Thus we realize that Lashon Hara is also one of the reasons the Beit Hamikdash hasn’t been rebuilt. If we do introspection we will realize that Lashon Hara is a result of baseless hatred, not knowing how to tolerate and accept each other. Finding flaws in others makes us feel superior, and make us believe that we have the right to judge others. Judging others is a result of being arrogant, which is compared to idolatry. Who would be the idol? Yourself. If we were humble enough (to see our own flaws) we would appreciate people’s good qualities instead of finding flaws and we will be able to learn to forgive.
"Kamtza bar Kamtza" - from the Talmud, Gittin 56 A man wanted to throw a party for all his friends, so he drew up a guest list and instructed his servant to send out the invitations. One of the men on the guest list was named "Kamtza," but the servant made a mistake and invited "Bar Kamtza" instead. Bar Kamtza was actually a sworn enemy of the host. When Bar Kamtza received his invitation, he was very grateful thinking that the fight was over between him and the host. But when Bar Kamtza showed up at the party the host asked him to leave. Bar Kamtza appealed to him by offering to pay part of the party. He pleaded numerous times, he even said: "I'll pay for the entire party! Just please don't embarrass me in this way!". The host, however, stuck to his guns and threw Bar Kamtza out. No one in the party said anything to defend bar Kamtza. The Talmud reports that Bar Kamtza was so hurt and upset, that he went straight to the Roman authorities and gave slanderous reports of disloyal behavior among the Jews. This fueled the Romans' anger, and they proceeded to attack and destroy the Holy Temple (which also brought poverty and deaths among the Jews).
From this we can realize the power of embarrassing someone (which is a way of Lashon Hara). The host spiritually killed Bar Kamtza by embarrassing him, and ultimately it caused physical destruction as well. When Bar Kamtza went to the party he was happy because he thought the hatred among them was finally going to be over. However, the host’s arrogance (which is a form of idolatry) fueled the fight. This also made Bar Kamtza create lashon hara to the Romans about the Jews, he didn’t forgive him. No one in the party did anything to defend Bar-Kamza. Maybe they were afraid to say something, but that was like agreeing with the host. This is why R. Chafetz Chaim advises us to avoid places where there is Lashon Hara, and to rebuke those who do it. From something that we think is so small a whole tragedy aroused.
We haven’t been able to learn to appreciate Hashem’s creation. We were created Betzelek Elokim, thus we must realize every person is intrinsically good and has a holy soul. Since we don’t have the omnipotence that Hashem has, we are unable to read someone’s heart or mind, and guarantee things as facts. This is why we should always give the benefit of doubt and also forgive. G-d is superior to all of us, who are we to judge His creation? Furthermore, Hashem looks at the scale we use to measure others. And with that same measure, He measures us!!