It was a perfectly human reaction, and it fit Sisko's character at the time. He was still angry, bitter and hadn't realized how far he'd fallen as a person. The whole Prophets thing made him realize he had to let go and accept what his life had become, accept pain and loss as part of the human experience, etc.
The novelization of Emissary made it clear that Sisko felt awful over how he treated Picard and realized that Picard was just another victim of the Borg and didn't deserve any hatred from him.
The novelization of Emissary made it clear that Sisko felt awful over how he treated Picard and realized that Picard was just another victim of the Borg and didn't deserve any hatred from him.