Remember, everyone's on the same team, even when things get heated. Steer the debriefing toward a positive conclusion. Make it a unifying learning experience. If consensus on certain issues isn't possible, correct this through future training and debriefings, to ensure the team stays on the same page.
Interesting perceptions sometimes come out of debriefings, sometimes from the least likely sources. A good example is a debriefing following a nasty hostage situation we handled. A wife shot and killed her husband who was sleeping in bed, and seriously wounded her two young children and herself. She then barricaded herself in a bedroom, holding the wounded children hostage.
Time was definitely not on our side, and rapid hostage rescue was the only viable option. Soon after arrival, the entry team made a hostage rescue, freeing the children, who survived. The female shot herself again, then fought fiercely with the entry team, and died en route to the hospital.
The debriefing was especially heated coming from an unexpected source: the cover and containment team, who were frustrated over what they perceived as "taking too long" to rescue the seriously wounded children. Their underlying frustration was having to stand by, doing nothing, waiting for the entry team to make the hostage rescue. In contrast, the entry team was too busy planning and making the rescue to think about anything except the rescue. Lesson learned: always include the entire team in debriefings, including those not directly involved, because you're all on the same team.
Sometimes debriefings result in changes in tactics and or training. A prime example was a call-up debriefing debate about the role of cover and containment when a suspect comes out, running full speed, hands empty. Bogged down by weighty equipment, cover and containment is no match for a fast-moving, determined suspect. As a result, cover and containment tactics were revised.