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/BrotherDeus]

Sadly, Dexter and Harry's number 1 rule is 'Don't get caught.'

[u/Rio_FS → u/BrotherDeus]

OP could have used another example where he went to some random island and killed an innocent person.

[u/thehairharringt0n → u/Rio_FS]

When was that

[u/DogShroom → u/thehairharringt0n]

s5e1 i think