The Gemara tells us that the Beis HaMikdash was destroyed because people were makpid on each other and treated them according to the strict letter of the law. This seems very difficult to understand - it would have seemed that the whole concept of going beyond the letter of the law is something of a stringency and that failing to follow it would not deserve such a strict punishment. Why were the Jewish people treated so harshly for being medakdek on each other?
In order to answer this question, it is first necessary to identify the Torah source for going beyond the letter of the law. In Parshas Va'eschanan, the Torah states: “And you will do that which is right and good in the eyes of Hashem so that He will do good to you and you will come and inherit the land which Hashem promised to give to your forefathers.” This teaches us of the necessity to avoid being medakdek (exacting) in matters of law and to be mevater (forgiving) what is rightfully ours in certain situations. One example of this is; when a person finds a lost object that halachically he is allowed to keep, but he knows the identity of the original owner - Chazal tell us that even though it is technically permitted to keep the object, he should nonetheless give it back. Another example is when a piece of property is for sale - the prospective buyers should give precedence to the person who lives next to that property because he stands to gain the most by buying this particular property. In truth, however, there are numerous instances when one should go beyond the letter of the law - the Ramban writes that the Torah did not want to explicitly state them all, rather we should learn from this passuk that we must constantly strive to treat people in an understanding fashion and avoid always treating them according to the strict letter of the law.
It seems that failure to treat people ‘beyond the letter of the law’ reflects a deep flaw in a person’s attitude to Avodas Hashem. My Rebbe, Rav Yitzchak Berkovits Shlita explains, (based on the Ramban on this passuk) that ‘v’asisa hayashar vehatov’ is the bein adam lechaveiro equivalent of ‘kedoshim tehyu’: The Ramban in Parshas Kedoshim explains that a person can keep all of the mitzvos and yet be a menuval b’reshus HaTorah.’ - this means that he is careful not to transgress any mitzvos but at the same time he has no interest in elevating himself in areas of reshus such as eating and sleeping. The underlying reason behind his lifestyle is that he believes that the Torah is true and therefore must be observed, but he does not subscribe to the true Torah outlook - he has no interest in elevating himself spiritually, rather his goals are very much ’this-worldly’, involving such aims as fulfilling his physical desires and attaining wealth. Because of his recognition of the truth of Torah, he will never deliberately commit aveiros, nevertheless he will show no interest in elevating himself in areas that he is not technically obligated to do so.
Similarly, in the realm of bein adam lechaveiro, a person may recognize the necessity of following the laws of the Torah, however he has no desire to integrate into himself the hashkafos behind them. Thus he will always adhere to the strict letter of the law but whenever he has the opportunity to make a financial gain in a technically permissible fashion he will not hesitate to do so. The Torah tells this person that he is making a serious hashkafic error by instructing him to “do what is right and good”, to act ‘beyond the letter of the law’, to treat people in a merciful fashion, and not be medakdek in every case. The Torah is instructing us that we should develop a genuine sense of ahavas Yisroel and thereby treat our fellow Jew in the same way that we would want them to treat us - to be forgiving and compassionate. Thus, for example, when someone has lost a valuable object, a Jew should not hesitate to return it even if he is not obligated to do so. Or, when a person is owed a large amount of money by a pauper, he should act with a degree of flexibility and compassion.
This helps understand why there was such a strict punishment when the Jews treated each other in a strict fashion - they missed the lesson of ‘hayashar b’hatov’, that it is not right to treat one’s fellow Jew in a harsh and unforgiving manner this does not adhere to the spirit of bein adam lechaverio that theTorah espouses.
The commentaries find another difficulty with the Gemara saying that the Beis HaMikdash was destroyed because the people were strict with each other. Other Gemaras give different reasons for the destructions, such as murder, idol worship, immorality and baseless hatred. Rav Yitzchak of Volozhin answered this question when he was witness to the following incident. Someone had slandered his fellow and now came on Erev Yom Kippur to ask for forgiveness. The victim refused to forgive him, pointing to the halacho that one does not have to forgive slander. Rav Yitzchak asked him about the aforementioned contradiction in Gemaras. He explained that the Batei HaMikdash was destroyed because of the terrible sins enumerated in the other Gemaras. However, he pointed out that Chazal tell us that when people treat each other beyond the letter of the law and are not makpid on every point, Hashem acts measure for measure and is forgiving for even the most serious sins. However, when Hashem saw that the people were treating each other in a strict fashion, He acted accordingly and chose not to be forgiving for their other sins. So too, Rav Yitzchak said to the unforgiving person, if you treat your fellow in such a medakdek way then you should expect that Hashem will treat you in the same way. The man heard the lesson and forgave the slanderer.
May we all be zocheh to treat each other how we would like to be tr
 Bava Metsia, 30b.
 Va’eschanan, 6:18.
 Bava Metsia, 30b.
 Bava Metsia, 108a. This is known as, ‘Din d’bar metsra.’
 Ramban, Va’eschanan, ibid.
 See my piece on Parsas Vayeira about how Lot epitomized this dichotomy.
 It is not clear which Beis HaMikdash the Gemara in Bava Metsia is referring to.
 Many other commentaries explain this Gemara in a similar vein to Rav Yitzchak, including the Maharal, Ben Yehoyada, and Chofetz Chaim.