He was brainwashed into being diehard for the cause since she was young. Her father apparently died during WWII, the mentioned it back in season 1 I believe. So he's always wanted to serve mother Russia. Phillip on the other hand is more idealistic, so he sees the hope in his kids not having to live in the world he lived in back in the USSR.

I think it's always been this back and forth with Phillip and Elizabeth on being down for the cause. He's been wanting to defect since the first season.