Disagreement is necessary to solidify agreement.
All individuals in a group agree on an issue without analysing its pros and cons. They arrive at a conclusion quickly and smoothly. But it is not the right approach, and in many cases the outcomes are not in sync with targets. 
All individuals have their own styles of thinking, their own action plans, and their own modes of execution, and it is rare to reach fruitful consensus at any level of functioning until the matter is thoroughly probed. 
When arrangements are made to force others to agree on the ideas of the group head, they are likely to be full of errors. All members must be given opportunities to express themselves freely so that the merits and demerits of projects or anything else are known to all participants. 
Diversity of opinions is a boon, not a barrier, in decision-making processes. It helps to reach a point of agreement more accurately in almost all conditions.
Even when views are at 180 degrees, efforts are required to find the middle point without losing sight of the grand purpose. It is possible when systems are in place. 
Regardless of cadre, ranking, or position, all members deserve to be heard before arriving at conclusions. More minds are likely to expand the areas of focus, but it also ensures more clarity on the matter and takes all safeguards into consideration. 
Most of us are not accustomed to listening, and the roots of many problems originate here. Practising listening is not a waste of time but an opportunity to know the unknown dimensions.