How can it be a good thing to do?
(א) וַיְדַבֵּ֥ר יְהֹוָ֖ה אֶל־מֹשֶׁ֥ה לֵּאמֹֽר׃ (ב) דַּבֵּר֙ אֶל־בְּנֵ֣י יִשְׂרָאֵ֔ל וְאָמַרְתָּ֖ אֲלֵהֶ֑ם אִ֣ישׁ אֽוֹ־אִשָּׁ֗ה כִּ֤י יַפְלִא֙ לִנְדֹּר֙ נֶ֣דֶר נָזִ֔יר לְהַזִּ֖יר לַֽיהֹוָֽה׃
(1) כי יפלא means, IF HE CLEARLY UTTERS (cf. Rashi on Leviticus 22:21 and Note thereon). — Why is the section dealing with the Nazarite placed in juxtaposition to the section dealing with the סוטה? To tell you that he who has once seen a סוטה in her disgrace should abstain from wine, because it may lead to adultery (Sotah 2a).
(9) If someone dies suddenly nearby, defiling the consecrated hair, the [nazirite] shall shave the head at the time of becoming pure, shaving it on the seventh day. (10) On the eighth day that person shall bring two turtledoves or two pigeons to the priest, at the entrance of the Tent of Meeting. (11) The priest shall offer one as a sin offering and the other as a burnt offering, and make expiation on the person’s behalf for the guilt incurred through the corpse. That same day the head shall be reconsecrated;
(1) מאשר חטא על הנפש [AND THE PRIEST … MAKE EXPIATION FOR HIM] FOR THAT HE HATH SINNED BY THE DEAD — i.e., that he has not been on his guard against defilement by a corpse. — R. Eleazer ha-Kappar said, “his sin consists in that he has afflicted himself by abstaining from the enjoyment of wine (Sifrei Bamidbar 30; Nazir 19a).
(13) This is the ritual for the nazirite: On the day that the term as nazirite is completed, the person shall be brought to the entrance of the Tent of Meeting. (14) As an offering to יהוה that person shall present: one male lamb in its first year, without blemish, for a burnt offering; one ewe lamb in its first year, without blemish, for a sin offering; one ram without blemish for an offering of well-being;
As it is taught in a baraita that Rabbi Shimon HaTzaddik said: In all my days as a priest, I never ate the guilt-offering of a ritually impure nazirite except for one occasion. One time, a particular man who was a nazirite came from the South and I saw that he had beautiful eyes and was good looking, and the fringes of his hair were arranged in curls. I said to him: My son, what did you see that made you decide to destroy this beautiful hair of yours by becoming a nazirite? A nazirite must shave off his hair at the completion of his term. If he becomes impure before the completion of his term, he shaves off his hair and starts his term of naziriteship again. He said to me: I was a shepherd for my father in my city, and I went to draw water from the spring, and I looked at my reflection [babavua] in the water and my evil inclination quickly overcame me and sought to expel me from the world. I said to myself: Wicked one! Why do you pride yourself in a world that is not yours? Why are you proud of someone who will eventually be food in the grave for worms and maggots, i.e., your body? I swear by the Temple service that I shall shave you for the sake of Heaven. Shimon HaTzaddik continues the narrative: I immediately arose and kissed him on his head. I said to him: My son, may there be more who take vows of naziriteship like you among the Jewish people. About you the verse states: “When either a man or a woman shall clearly utter a vow, the vow of a nazirite, to consecrate himself to the Lord” (Numbers 6:2). This is an example of voluntary acceptance of naziriteship, i.e., becoming a nazirite with entirely pure intentions rather than as a rash statement, e.g., while in a fit of anger.
(א) שֶׁמָּא יֹאמַר אָדָם הוֹאִיל וְהַקִּנְאָה וְהַתַּאֲוָה וְהַכָּבוֹד וְכַיּוֹצֵא בָּהֶם דֶּרֶךְ רָעָה הֵן וּמוֹצִיאִין אֶת הָאָדָם מִן הָעוֹלָם. אֶפְרשׁ מֵהֶן בְּיוֹתֵר וְאֶתְרַחֵק לַצַּד הָאַחֲרוֹן. עַד שֶׁלֹּא יֹאכַל בָּשָׂר וְלֹא יִשְׁתֶּה יַיִן וְלֹא יִשָּׂא אִשָּׁה וְלֹא יֵשֵׁב בְּדִירָה נָאָה וְלֹא יִלְבַּשׁ מַלְבּוּשׁ נָאֶה אֶלָּא הַשַּׂק וְהַצֶּמֶר הַקָּשֶׁה וְכַיּוֹצֵא בָּהֶן כְּגוֹן כֹּהֲנֵי הָעוֹבְדֵי כּוֹכָבִים. גַּם זֶה דֶּרֶךְ רָעָה הִיא וְאָסוּר לֵילֵךְ בָּהּ. הַמְהַלֵּךְ בְּדֶרֶךְ זוֹ נִקְרָא חוֹטֵא. שֶׁהֲרֵי הוּא אוֹמֵר בְּנָזִיר (במדבר ו יא) "וְכִפֶּר עָלָיו מֵאֲשֶׁר חָטָא עַל הַנָּפֶשׁ". אָמְרוּ חֲכָמִים וּמָה אִם נָזִיר שֶׁלֹּא פֵּרַשׁ אֶלָּא מִן הַיַּיִן צָרִיךְ כַּפָּרָה הַמּוֹנֵעַ עַצְמוֹ מִכָּל דָּבָר וְדָבָר עַל אַחַת כַּמָּה וְכַמָּה. לְפִיכָךְ צִוּוּ חֲכָמִים שֶׁלֹּא יִמְנַע אָדָם עַצְמוֹ אֶלָּא מִדְּבָרִים שֶׁמְּנַעְתּוֹ הַתּוֹרָה בִּלְבַד. וְלֹא יְהֵא אוֹסֵר עַצְמוֹ בִּנְדָרִים וּבִשְׁבוּעוֹת עַל דְּבָרִים הַמֻּתָּרִים. כָּךְ אָמְרוּ חֲכָמִים לֹא דַּיֶּךָ מַה שֶּׁאָסְרָה תּוֹרָה אֶלָּא שֶׁאַתָּה אוֹסֵר עָלֶיךָ דְּבָרִים אֲחֵרִים. וּבַכְּלָל הַזֶּה אֵלּוּ שֶׁמִּתְעַנִּין תָּמִיד אֵינָן בְּדֶרֶךְ טוֹבָה. וְאָסְרוּ חֲכָמִים שֶׁיְּהֵא אָדָם מְסַגֵּף עַצְמוֹ בְּתַעֲנִית. וְעַל כָּל הַדְּבָרִים הָאֵלּוּ וְכַיּוֹצֵא בָּהֶן צִוָּה שְׁלֹמֹה וְאָמַר (קהלת ז טז) "אַל תְּהִי צַדִּיק הַרְבֵּה וְאַל תִּתְחַכַּם יוֹתֵר לָמָּה תִּשּׁוֹמֵם":
(1) Peradventure man will say: Seeing that envy, desire and vainglory and like tendencies are evil tendencies and remove man from life, I will separate myself from them exceedingly and reach their remotest extreme. Until he will eat no meat, drink no wine, marry no woman, dwell in no comfortable quarters, dress in no proper clothes but in a sack and coarse wool, and the like, as for instance the idolatrous priests do. Even such is an evil way, and it is forbidden to follow it. He who follows this way is called a sinner, for it is said of a Nazarite: "And make an atonement for him, because he hath sinned against the soul" (Num. 6.11), whereupon the sages said: "If the Nazarite, who did not separate himself from aught but wine must have atonement, he who deprives himself from each and every thing how manifold must his atonement be" (Baba Kama. 91b)! Therefore did the sages command, saying: A man shall not deprive himself of ought save the things which the Torah itself deprived him of; nor shall he bind himself by vows and oaths to abstain from things which are permitted. They have even said: "Is it not enough for thee what the Torah has forbidden, that thou doest forbid thyself even other things" (Yeru. Nedarim. 7.37)? And in this rule are included such who are continuously fasting, for they are not in the good way, and the sages prohibited one from punishing himself with fast days. Concerning such and like matters Solomon admonished saying: "Be not righteous overmuch; neither show thyself wise; why wouldst thou destroy thyself" (Ecc. 7.16).