Metzorah Therapy

The law is that a negah to be tamah or tahor must be pronounced by the kohan.  The Sfas Emes asks, I understood the tahara process should be done by the konanim for the metzorah hurt his/her friend though loshon harah, so the kohanim that embody chesed and shalom cause his tahara; but why must they cause the tumah?

The Kli Yakar in Tzaria (13:2) and at the beginning of Metzorah says the same idea (see there what he explains based upon it,) שהצרעת בא על עונות ידועים ושם המכה צרעת ושם המוכה מצורע, כי לשון מצורע מוציא רע שמוציא כל רעתו הנסתרת בקרבו אל החוץ לגלות רעתו בקהל ושם צרעת הוא לשון צרה רעה ר״ל רעה שהיא כצרה.  The source for this idea is at the end of Vayikra Rabbah (16:2) and alluded to in Arachin (15b.)  The Sfas Emes says there is a positive to affect to the tumah of the person coming out to the forefront.   A person that has טומאה ורע inside can't be cured; the toxins don't leave any room for holiness.  The advantage that the metzorah has is that s/he has taken out all the toxic from within and is left with a soul that is capable of being repaired.  That is why indeed the nega is a chesed for the individual to allow them to be on their path to recovery and indeed it is fitting for the kohan to be the therapist to help start the process of recovery. 

The מושב זקנים in 14:4 brings from the Rokeach that the two birds that the metzora brings are a hint to the yetzer tov and yetzer harah and killing one of the birds tells you that you must kill the yetzer harah.  The Sfas Emes also views the two birds as a hint to the two yetzers but as opposed to Tosfos that views the yetzer harah as a force which must be killed out, the Sfas Emes sees the positive in it.  [That is because the Sfas Emes wore a fury hat and they like to see the good in all things.]   He takes the opposite view; the bird which is sent away is the yetzer harah.  At their root both birds are צפורות טהורות, the yetzer harah also has tendencies that can be used for the positive, it is only after that is absorbed that the toxic dimensions are sent away.  [This isn't exactly how the Sfas Emes says it; it is inspired by his words; he seems to take different approaches in Tazria 6537 and Metzorah 5632.]
After going through nega therapy, the meztorah has learned to partition the parts of the yetzer harah and release the bad.

Based upon this, the Sfas Emes understands the Rashi at the beginning of Tazria in a different light. א״ר שמלאי כשם שיצירתו אחר כל בהמה וחיה במעשה בראשית, כך תורתו נתפרשה אחר תורת בהמה חיה ועוף.  It is only after the נפש הבהמית of the individual has been turned into a mentch; after its destructive behavior has been rectified; the torah of his/her inner animal has been elevated that one can release the potential of the אדם, אדמה לעליון.