that's what sensei wanted to point: there's no good ones or bad ones
they're both at fault at the same time and they're both to blame and both are victims
those who died when Eren chaged into a titan during the taybur's speech are just the same as those who died when Rainer and Berth broke the wall
eren only attacked after they declare war on island .. everything is fair in war .. it not immoral .. but it kill before you get killed situation
imagine a 5 y.o was there and saw his mother being crushed
what does it have to do with him? was he the one who declared war? why should he pay?
BUT as I said it's everyone fault in the end: staying neurtal and ignorant and not taking action is also wrong
this called collateral damage , forget about 5yr watching their parents death , their new or unborn babies who die on wars ..
we don't know who the good guy or bad is .. everytime we say he bad they do reverse sh0t yup