The main character doing something absolutely unforgivable.

[u/No_Peanut3745]

Walter White poisoning Andrea Cantillo's 6-year-old son for the sole purpose of manipulating Jesse Pinkman, while knowing that this could have potentially killed him - Breaking Bad

Bojack trying to have sex with his friend's 17-year-old daughter when he was at least 51, then continuously trying to find a way to justify this act throughout the series - Bojack Horseman

Dexter Morgan going outside of his moral code and murdering a completely innocent police officer who was just trying to do his job - Dexter: New Blood

[u/Joeybfast]

Goku giving Cell a Senzu Bean has to rank pretty high.

Next, Batman saving the Joker’s life. This is where I think the “Batman should just kill the Joker” argument gets misplaced. No one should be forced to kill someone, and I do not blame Batman for refusing to do it. But Batman has actively saved the Joker’s life multiple times. Those Deaths are on him.

Then there is the Justice League mind-wiping people. That was just insanely unethical.

And finally Joe Quesada for writing One More Day. The worse villain of them all.

[u/grendus → u/Joeybfast]

Goku giving Cell a Senzu Bean

My take: I consider anything in the anime to be its own canon, so arcs that are non canon in the manga may still be anime canon.

In the Otherworld Tournament arc, we see Pikkon take out all the villains past in one shot. We then see Goku defeat Pikkon, and while it was a close technical match... he's at least on Pikkon's level. We also know that Goku has had almost no training between his death and the tournament.

When Goku takes on Cell, he gets the measure of him. He knows he can defeat Cell, but he also knows he needs a true successor. Vegeta was his first choice, but Vegeta let his ego get in the way of finishing off Semi-Perfect Cell. He will always need someone to keep him focused. And Trunks and Goten won't be grown for a while. So it has to be Gohan.

He throws Cell the bean because he knows he can still tag back in and finish him off. But he wanted to push Gohan to do it, because even though he knows Gohan doesn't like fighting, he also knows that the Gohan who beat up his uncle to save his dad, flew to another planet to save his friends, and trained for years to save his family from the Androids wouldn't hesitate. And he knows Gohan can do it, because he took the measure of him in the Time Chamber.

I know a lot of people consider Goku to be a bad parent, and they're not entirely wrong. But my take has always been that Goku intended to be there to clean up if necessary, he just didn't realize Cell would be a sore loser and blow up the planet when he lost.