Your stance is that loving good or hating evil implies we are able to differentiate between the two, which is a stance of moral superiority. Jesus did not say we should never use judgment (discernment), he said don't judge others (i.e. don't be judgmental or a hypocrite). In fact, he commands us to fix our own faults first, which implies knowing the difference between good and evil, so we can see clearly enough to help our brothers.

I think the hang up is the way Aquinas phrased the last sentence "you are immoral as well as unjust." He is not condemning the reader, he is merely saying that it's a natural response of people with morals to get angry when they see injustice. It's more of an approval to have righteous indignation.