What is "Matzdik Rasha u'Marshi'a Tzadik"?
R. Yonah: "Omer la'Rasha Tzadik Atah Yikvuhu Amim" (24:24) is flattery. Here it discusses one who justifies a Rasha and advocates for his merit not in front of him. This is not flattery. Rather, amidst love of him, he is dear in his eyes.
Orchos Tzadikim (Sha'ar ha'Ratzon DH Af Al Pi): One who puts his desire to evil deeds, and is pleased with Resha'im and their deeds, and despises Tzadikim - this will bring him to the bottom pit (Gehinom).
Malbim: After a judge knows who is innocent and who is liable, and he makes a compromise, via this he obligates a Tzadik. He is worse than one who vindicates a Rasha 1 . The Rasha takes some of what does not belong to him, and the Tzadik loses some of what belongs to him.
I.e. he exempts a Rasha, but does not force a Tzadik to pay. (PF)
Why are both of them an abomination?
R. Yonah: One justifies a Rasha due to love of him. One must hate enemies of Hashem - "ha'Lo Mesan'echa Hashem Esna" (Tehilim 139:21) and disgrace them - "u'Vozai Yekalu" (Shmuel I, 2:30). Not only does he not hate and disgrace them - he loves, honors and justifies them! Honoring Resha'im strengthens the hand of sinners, and people do not despise the sins and scorn sinners. Also the Rasha's hand will rule do not the honor, and his words will be heeded and many will be drawn after him. This also lowers the honor of Tzadikim and Chachamim; they will not have power to return many from sin - "v'So'avas Rasha Yeshar Derech", "Beis Resha'im Yishamed v'Ohel Yesharim Yafri'ach" (29:27, 14:10). When Resha'im are honored and Tzadikim are lowered, people do not glorify Avodas Hashem. This causes the loss of Nefashos, for Hashem created the world for His honor - "Kol ha'Nikra vi'Shmi v'Lichvodi Berasiv Yetzartiv Af Asisiv" (Yeshayah 43:7); "Ki Zeh Kol ha'Adam" (Koheles 12:13).
What does "Gam" come to include?
R. Yonah: Even though one who condemns a Tzadik is worse than one who vindicates a Rasha, also the latter is To'avas Hashem.