Ron Jeffries explains why software quality and speed of delivery are not mutually exclusive. If you want to continually deliver working software quickly, then you need to maintain high quality:
Uncle Bob has also posted his thoughts:
I often find there is a lot of focus on delivering software quickly, but not so much on maintaining quality. I think this is because it is generally considered that maintaining high quality means greater expense and later delivery. However, the higher the quality of code, the better able we are to deliver working software quickly and repeatedly. My belief is that the quality leaver should never be touched, or you risk taking on crushing debt.