You know, i've seen a lot of Accel hate, but i was always convinced he was alright. Did he look down on Pro-Heroes? Yes. Was he wrong to? Yes.
But just because you're wrong doesn't mean you're stupid.
(Webcomic Spoilers)
Not when i really can't blame him for thinking that way. We've seen it ourselves: the Hero Association is a dirty business. Fraud, monster and human trafficking, illegal gambling, media manipulation, bribery and blackmail. In the Manga McCoy was even gonna let gonna let a police station get destroyed by a rogue monster.
What are the chances something similar happened when Accel's vigilante group lost a few of it's members taking down a Demon? Such an experience would turn anyone bitter.
It's not strange for Accel to assume the S-class would be in on it and to fair it's not entirely wrong. Most top heroes are complicit, they are aware the HA is at least somewhat shady, but most hold their nose and look the other way. Call it the cost of doing business, they've got bigger fish to fry. (Don't bite the hand that feeds you) Some might even say this sort of thing is beneath them.
And underestimating the S-Class strength? Well the Hero-Association misclassifies monsters all the time. In the Manga we've seen them do it intentionally and even make up Monster Attacks out of whole cloth. A few bad drops quickly poisons the whole well.
Then Accel gets taken in by the Neo-Heroes and they tell him everything he wants to hear they probably even expose some of the wrongdoing of the HA to him. Is it naive? Sure. But i don't think that makes him a bad guy.
Lets be honest: when Accel found Tank Top Master, it was bad look. Most members of the HA think TTM is just a hooligan even on a good day and this was not a good day. And Accel's words might have been overly harsh, but he was right. With the information they had, it was more sensible for Accel's group to fight the Robots directly while TTM and his gang coordinated the evacuation. Accel didn't know just how strong TTM really was.
Tank Top Master, being the GOAT, could read past the emotion in a tense situation and take the Accel's advice for what it was. Notice when he does save the day here, it seems he left his gang behind.
Accel might not have much fight left in him after being forced to fight his own comrades, but a stone can still be a treasure and Accel will still make the most of it. Even if it's like squeezing water from one.
Aside from not being a bad guy he's also really not a bad guy, is what i'm saying.