you're wrong even if you're right - the lesson of Korach's rebellion

Moshe told Klal Yisrael that if Hashem makes a hole in the ground to swallow up Korach, that proves Korach is a rasha and guilty of instigating rebellion.  But,  אִם ־כְּמ֤וֹת כׇּל ־הָֽאָדָם֙ יְמֻת֣וּן אֵ֔לֶּה וּפְקֻדַּת֙ כׇּל ־הָ֣אָדָ֔ם יִפָּקֵ֖ד עֲלֵיהֶ֑ם לֹ֥א ה׳ שְׁלָחָֽנִי, if Korach dies a normal death, then that proves Moshe is in the wrong. It sounds like either way, Korach is going to die.  The only question is whether he is going to die a normal death like anyone else, or whether he is going to be swallowed up by the earth.  

If Korach was in the right and not guilty of rebellion, why should he be chayav misa?  The test should be whether Korach is swallowed up or whether he lives l'arichus yamim v'shanim?  (See Malbim)  

The Yitav Lev answers that we see from here that even if all of Korach's claims against Moshe had merit, he was still chayav misa.  You can have taanos, arguments, machlokes, but there is right way and a wrong way to disagree.  Beis Shamai and Beis Hillel had many arguments, but they fulfilled הָאֱמֶת וְהַשָּׁלוֹם אֱהָבוּ.  They argued with civility.  Korach argued in a way that disrespected and undermined the kavod of Moshe Rabeinu.  Therefore, he was chayav.  The only question is whether his chiyuv was purely for the lack of respect, or whether the complaint itself was invalid and kefira.

Korach wrapped his arguments in idealistic rhetoric, "ki kol ha'eidah kulam kedoshim...," and may have even thought his rebellion was a mitzvah.  On some level he may have sincerely wanted to serve Hashem as kohen gadol.  The same is true of many misguided people who think their campaign, whatever it may be, is a mitzvah, but in reality, it's the exact opposite.  How can a person know when what they are advocating is truly mitzvah and truly l'shem shamayim vs when they are just fooling themselves or being fooled by the yetzer ha'ra?  

Agra d'Kallah writes:

 והנה הסימן על זה אם הוא באמת מצוה או אם הוא מתרמית היצר, הוא כשיבחין האדם בעצמו אם גדלה תשוקתו כל כך לשאר המצות גם כן, לאותן העניינים שהם בודאי מצוה כגון ציצית ותפילין ותורה אזי הוא טוב. אך אם רואה שאינו משתוקק כל כך לשאר המצות, יבין לאשורו שהתשוקה הזאת שמדמה בדעתו לאותו ענין הנרצה לו למצוה, הוא מפיתוי היצר להפילו במכמורת, ותחתיה תעמוד הבהרת, כך קבלנו.

If a person has equal enthusiasm for all mitzvos and all good causes, then they can rest assured that the particular cause they are fighting for at that moment is just.  However, if a person has their one hobby horse, their one cause, to the exclusion of other good causes that are not on their radar, then that's their own fight, it's not a l'shem shamayim fight.  

Agra d'Kallah goes on to give some other good advice about the dangers of jumping too zealously on that hobby horse.  David haMelech says in Tehillim (86:2) שָׁ֥מְרָ֣ה נַפְשִׁי֮ כִּֽ ־חָסִ֢יד אָ֥֫נִי  The simple pshat in the pasuk is that David was asking for Hashem's protection in the merit of his being a chassid and going above and beyond.  The Agra d'Kallah derech derush suggests a different interpretation.  A regular person can measure whether they are doing the right thing by looking in the shulchas aruch. For the chassid, who goes lifnim mi'shuras ha'din, that's not good enough.  If you tell him that it says in shulchan aruch X, he can always answer that that's just the letter of the law, but he wants to do more.  Agra d'Kallah gives an extreme example of someone who is so machmir on chameitz that no matzah is kosher enough for him, and as a result he never fulfills the mitzvas aseh.  שָׁ֥מְרָ֣ה נַפְשִׁי֮ כִּֽ ־חָסִ֢יד אָ֥֫נִי says David haMelech, because davka a chassid needs extra protection to make sure he doesn't get carried away with his zeal and enthusiasm.  Davka someone who operates outside the lines, outside the shuras ha'din, needs protection to make sure it is done in a positive way for a positive and just cause.