"The 100" and POV

Reasons Why the Ambush on the Grounder Army was Justified (not right, but understandable from Arkadia's position):

(1) There is no reason to trust an "ally" who already betrayed you and left you to die. There was an alliance, and Lexa broke it, so why should Arkers just readily believe that, oh, she means it this time? (And her devotion to Clarke doesn't count. Arkers have no idea what went on in Polis. Clarke, Kane, & Abby made the decision to become the "13th Clan" without any input from their people, who had been hurt by Grounders repeatedly since they landed.

(2) Even if Lexa did intend to protect SkyKru, she did not have the power to do it. She lost the faith and support of her people, the Coalition ambassadors tried to remove her as Heda, & most of the Clans rejected or wanted to kill SkyKru. This and the Ice Nation attack on Mt. Weather proved that Lexa could not control the army she sent, even if she sent it to protect Arkadia.

(3) So Arkers can't trust Lexa to keep her word or to keep them safe. Instead, all they see is an army of "peacekeepers" on their doorstep, which is easily seen as a threat or an act of oppression. An army of Grounders who are just as mistrustful/prejudiced/hateful of SkyKru as Arkers are of Grounders. There's no guarantee that the Grounders won't defy Lexa and destroy the Ark civilization. The claim of 4 leaders (Clexa & Kabby) who no longer speak for most of their peoples, is not enough to change months of war and betrayal into a true alliance of peace.

(4) In fact, Arkers were right to fear the army camped outside, because after Lexa died, the army would have turned on Arkadia and wiped them all out without warning. Ontari said as much, and anyway, most Grounders wanted to. The truce was a powder keg that would have exploded into full-blown war again if they hadn't united for the ALIE threat.

Was it wrong to massacre the army? YES. (And Bellamy struggled with it the whole time, the same way ALL the characters do when they do something bad "for the greater good.") Was it done without reason though? NO. They had legit reasons, and they felt they had no other choice (again, same as every character's motivation). Just like what Clarke and Bellamy did at Mt. Weather, Bellamy knew it was wrong but did it anyway to protect his people and took on the burden of guilt, like Clarke said, "I bear it so they don't have to."

The 100 is all about moral ambiguity, and "there are no good guys," which means there are no bad guys either, just people trying to protect their people. Each season's "Bad Guy" has not been evil, just standing on the other side with a different perspective of what is "best" for people.

Furthermore, Arkers and Grounders are held to different moral standards by the audience. Arkers are more like our society and therefore more relatable, while Grounders are a warrior culture from a harsh, post-apocalyptic Earth where "Blood Must Have Blood." Grounders wiping out their enemies is awesome in a Game of Thrones/300 way, but Arkers removing a very real, direct threat (1 army of many) is sickening to our modern sensibilities. (To be fair, killing an armed militia--a real threat--is NOT the same as gunning down innocent civilians--an imaginary threat.)

Pike & Co. had been victims of so much violence that they felt that the only way to survive was to be as ruthless as the Grounders (Ice Nation). So it makes sense that they would use a despicable night ambush with guns against swords. I personally feel that it was out-of-character of Bellamy (even w/ PTSD) to go along with the plan. I expected him to just warn the army to get off Arkadian lands before fighting broke out, but it should be noted that he tried to save the wounded, but Pike killed them.

Bellamy IS partially responsible, and everyone does hold him responsible, including himself, just like Clarke IS partially responsible for Tondc too. Just because she didn't launch the missile herself doesn't excuse her failure to save everyone there when all she had to do was warn them. And why is the death of 1 Grounder army to protect ALL of your people "unforgivable," but the Mt. Weather genocide (killing every man, woman, & child) to save a group of friends "justified"? These are the kind of impossible moral questions that The 100 asks, and the answer is always, "It depends on your point of view," even when it's hard to see characters' POV. The point is to try. "There are no good guys."