When I coach designers who are bracing themselves to “defend their design”, I first make them understand that a design review is not a zero sum negotiation. It is not about one party winning and the other losing. In fact, when that happens, it turns out everybody on the team loses. They lose trust, become adversarial, and moving the project forward becomes difficult. These design reviews should be thought of as integrative, or interest-based negotiations. Chances are, everybody wants the design to be successful, they just have different ideas of what that means.
So when presenting your design, tell the audiences why you designed something the way you did and what drove you to take that approach. Focus on the underlying interests. Ask the audiences if they share those interests. Find common ground with your audience and then discuss the details of your design. Be open to hearing their concerns and ideas for the design and use the backdrop of shared interests to justify your decision to accept or debate new ideas.
Getting your audience to acknowledge common interests and goals of the design will go a long way to avoiding the biases, ego and agendas that oftentimes derail design reviews.