(picks up microphone) goro akechi is hated very little for the character he is and moreso for the things he stands for.
part of the reason goro akechi is such a vilified character despite being a very common anime trope of young/child hitmen/villains is because he's heavily gay-coded in a series that, to this day, is heavily homophobic and transphobic, and has many homophobic and transphobic fans. if goro was a woman or was written as straight, he would be just as popular and loved as any other character of his trope, something that has been literally stated by those who actively hate goro (yes, i have screenshots for that).
furthermore, smt fans (and really, anime fans in general) seem to have very little to no grasp on how abuse works, or even outright hate abused characters for not being the buff, womanizing 'man's man' of the week cishet men look for in anime. this is why shido, his abuser, is also seen as not at fault - and, furthermore, why rapist-murderer adachi is so popular among goro haters despite ALSO not having a good motivation for murder.
finally, in a more specific example, goro is the only character in persona 5 who actively wishes to ruin his abuser - this doesn't make him a bad person, it makes him a survivor. that's how we feel, oftentimes, and that anger never really goes away. this does tie in to my second point, but generally speaking i feel its telling that NONE of the other thieves are vilified for their anger - not ryuji or ann, who wished to kill kamoshida. not yusuke, who, in a fit of anger, wished misfortune on madarame. not haru, who openly sympathizes with goro for his anger at how the world has treated him. only goro, the strongest gay-coded character and the only one to harbor such a strong anger (and a well-deserved one, at that.)
this all stems from the inherent lack of understanding of abuse victims, and, paratially, the cishetmormativity of anime fans that, to this day, runs rampant. welcome to my ted FUCKING talk