I recommend to tell that manager to learn about how people can be motivated, because yeah, deadlines are one kind of motivation, but there are a huge amount of people who responds much better to other kind of motivations.
I've seen similar things said by Duke Ellington and Kevin Kelly.
I think the reasoning KK gave was the deadline will force you to drop all the unnecessary cruft to focus on delivering the essential as fast as possible.
I once gave a version of this to a manager and he replied by telling me that nothing gets done without a deadline.
He kinda made a point. Curious to see what people think about this?