There's nobody on the X-Men who works harder than Scott Summers, aka Cyclops. Years of training has allowed the visor-wearing mutant to become a master tactician, a gifted fighter and a fantastic leader. Because he's strict and a stickler for rules, Scott regularly clashes with his more brash colleagues, especially Wolverine, which creates a lot of banter and conflict on the team.
Even though he's often portrayed as the voice of reason, Cyclops has performed some immoral acts over the years, making him come across as utterly despicable.
When his wife Madelyne Pryor believed she lost her son, Scott abandoned her to be with Jean, which caused Madelyne to go insane. Years later, he cheated on Jean with Emma Frost. After Jean was killed, Scott made out with Emma... at Jean's grave! Who does that?
More recently, he lost his mind after being possessed by the Phoenix, causing him to kill his mentor, Professor X. Although Scott's actions were manipulated by the Phoenix, he justified his actions after the cosmic entity left his body.
The moral of the story is, if you want a hero to come across as likeable, don't make them justify murder. That's like Superhero 101.