When Katniss agreed to continue the Hunger Games using Capitol children (as a tribute to Prim), I thought that she was lying, tricking Coin into believing that she supported her and her ways and didn't believe that Coin was in any way guilty of Prim's death.
However, I think that Katniss had just been given the final proof that Coin was just as bad as Snow and that she was willing to sacrifice innocent children in order to gain control of their world.
In other words, Snow had told the truth about Prim's death and it was Coin who was responsible. I believe that this epiphany is important because it shows that Katniss wasn't just vengeful but still thinking in a strategic way about how to make their world better.
I believe this epiphany and her previous conversations about how she should trust no-one, and that she needed to prove her loyalty to Coin if she wanted to live etc. convinced her to lie and say that she wanted the games to continue.
This meant that she would earn a little bit of trust from Coin, which would giver her the chance to get close to Coin and kill her, which she does.
However, no-one else I've talked to sees it my way. Everyone else thinks she was just reacting from hopelessness, anger, revenge etc.
What does everyone else think?