When we have a conversation about a topic close to our identity (vegetarian/meat eater, nationality, race, gender etc) we automatically go into defense mode.
Our identity is possibly being attacked and we add emotion to the conversation. This causes the conversation to be less effective or constructive.
When you feel you're about to respond to a topic with your identity, recognize that emotion. Single it out and decide to disregard it or to not engage in the conversation.