The scenario: You're a Scrum Master, you're in a sprint planning meeting and another team member raises an issue. You disagree that it's an issue and don't think we should allocate extra time to deal with it. Your colleague disagrees vehemently and you suddenly find yourself in a showdown.
How do you handle it? Well you could continue to argue your point. You could try to compromise and allocate some time. You could cave and say fine, allocate whatever you want. The problem is that when trying to deal with issues where we are in conflict with our team, our ego gets in the way. So try this - park your ego at the door, and leave it there until you are ready to go home. As soon as you forget to leave it at the door, the team runs the risk of being a team only when you are in agreement with each other.
It's hard to park your ego, but as a Scrum Master you have to show the way. And as soon as you park the ego, other options will appear. It's a little like getting out of your own way to allow that brilliant idea to make its way to the front of your brain.
Incidentally, how I would likely deal with the above scenario is to calmly regain perspective, then remember what we are doing. i.e. what is our Sprint Goal, what is the value of the option we are discussing to the sprint and the product. The idea is to see beyond our own pettiness and evaluate the issue in the context of what is right for the product and the team. If this process does not resolve it then open it up to the team for their input and advice. The consensus holds.