Hank McCoy, aka Beast, is an iconic member of Marvel's premier mutant team, debuting in Stan Lee and Jack Kirby's very first issue of X-Men in 1963. From his roots as a happy-go-lucky student at the Xavier Institute, the Beast has made much progress, becoming an esteemed professor and even joining the Avengers.
However, the Beast has been continually pushed over the edge, making so many morally questionable decisions. It therefore seems unlikely that the irresponsible genius can ever fully redeem himself. Beast's descent into darkness began with his desire to develop a cure for the Legacy Virus. Believing that he should be able to solve any solution with time and effort, Beast's pursuit of a cure became an unhealthy obsession.
The Beast's Obsessive Nature Caused His Downfall
The Beast's obsession with the Legacy Virus led him to do something almost unthinkable for a hero. After Hank discovered that Threnody could use her mutant powers to see the effects of the Legacy Virus on others, he handed her over to one of the X-Men's worst antagonists, Mr. Sinister. The villainous scientist possessed better resources than the Beast, and lacked any morals that could stand in the way of his research. This would be the first of many steps that the founding X-Man took away from his heroic path.
Later, in 2007's Endangered Species (by Mike Carey and Scot Eaton), Beast tried to reverse Scarlet Witch's eradication of mutants that took place on M-Day. Rather than going to his friends, Beast sought the help of the world's most ingenious villains. He even aligned himself with the evil alternate reality version of himself, the Dark Beast. Additionally, Beast joined the Illuminati and supported the destruction of entire universes in order to save their own. Their actions of the group were so reprehensible that Captain America himself opposed them.
The Beast Has Reached the Point of No Return
Beast hit a new low in All-New X-Men (by Brian Michael Bendis and Stuart Immonen), where he meddled with the fabric of time by bringing the original X-Men into the future. Although Beast did this in the hopes of doing something good before he died, the reasoning for his actions was not just reckless and petty, but also tried to force an easy solution to a complex problem.
In recent issues of X-Force, many of the Beast's actions have put him in direct opposition with the rest of the team. Issue #12 saw Beast advocate for turning Krakoa into a police state, wanting to detain any mutants with ties to Russia, including his own teammate Colossus. While he did eventually apologize to Colossus, Hank still continued going down a dark path, considering turning Krakoa's mutations into a dirty bomb, and transforming his longtime teammate Wolverine into little more than a mindless weapon. At this point, even though Hank McCoy believes he still has his moral compass, it is truly gone.