You get the scene. You are pitching to a group of senior executives.
It has taken months to set this up, and you are finally there. The section head has asked you for this pitch so you walk into the room carrying a bit of political weight. (E.g. you have the right to be there)
And then it starts. For some reason or another someone in the audience is intent on playing the role of spoiler. Cutting down your comments, making claims that "we are already doing this" and trying to make sure that the pitch falls over.
Bad situation. But not that uncommon.
You can either meet each challenge that is posed. Refuting it or proving it wrong.
Or you can let it ride.
I far prefer the first, but the second is more likely to achieve better results.
The leaders you are presenting to are not stupid. They will see this for what it is, and will only take half notice of it. But if you flare up then all is definitely lost.
Control of ego is probably the hardest thing to do as a consultant. Particularly when you are certain that you can offer scarce and valuable assistance.
Your best option? Thank him for his criticisms. Make it clear that there were probably others in the room who didn't see things with his clarity. And try to treat the whole thing as objectively and calmly as possible - without trying to win the upper hand on any issues.