Musar zu Kohelet 9:5

And it is likely that the case of the one praising the evildoers is from foolishness. For the fool (he) intends to praise the good - whether it is about the truth, or whether it is the opposite. And without knowing, he is praising the dead. For our Rabbis said (Berakhot 18b), [that] evildoers are considered like wraiths, as it is stated (Ecclesiastes 9:5). “But the dead know nothing.” But this unintentional sin is considered wanton. For a master would not love a slave, if [the slave] loves [the master’s] enemies and brings close those who he has distanced. Should they not know this from the intellect, that this is so? And it is stated (Proverbs 3:35), “disgrace uplifts dullards.”