My heart cries out over [the downfall of] Moab…
The prophets of Israel are not like the prophets of the nations of the world. Balaam (a gentile prophet, see Numbers 22:2-24:25) sought to uproot Israel over nothing, but the prophets of Israel mourn over the retribution that befalls the nations.
I make no comment here as to whether this is good or bad (Rashi makes no comment to this effect either, though the implication is that Rashi is not criticizing the prophet Isaiah), but it seems to be the undying trait of the Jew to love and feel compassion and act mercifully toward those who would kill us given the chance. Let no one think that ours is the first generation to behave this way.
“Therefore my loins are filled with trembling, pains have taken hold of me like the pangs of one giving birth, I have become ill from hearing, I am terrified from seeing.”
This verse comes during a prophecy regarding the downfall of Babylonia, the cruel empire that destroyed Judah and exiled the Jews, not someone the Jews should necessarily feel compassion for. Yet:
“The prophet is compassionate and grieves over the calamities that befall the nations.”
-Rashi, citing Midrash