The 100 Creator Defends Bellamy's Betrayal

There are accusations that Bellamy - who knows firsthand the guilt that comes with committing genocide - would not support and participate in Pike's mass murder of Grounders, particularly Grounders who were sent to Arkadia as allies and protection.

[...] while Bellamy has expressed his doubts regarding Pike's methods and went out of his way to spare Indra's (Adina Porter) life, he ultimately has continued to follow Pike's orders, even going so far as to betray Clarke (Eliza Taylor) and Lincoln (Ricky Whittle).

Rothernberg is quick to point out that while we, as an audience, have spent intimate time with Grounders, Bellamy has not shared these experiences.

[...] for Bellamy, you add on to that ... the explosion of Mount Weather in Episode 3, the loss of all of those people who he was there to protect ... and of course, there was a little bit extra heartache for him because [Gina] was killed as well.