The wisdom of crowds postulates that on the long term group decisions are better than those made by the smartest single member of the group. In general the more diverse the opinions and the more independent the members of the group are the better the decision will be. This applies to all areas of life except for one: creativity. Commitees almost never come up with good creative solutions.
Different ideas various people hold can be compared to a large gene pool in a population. In a homogenous population a sudden environmental change or a new disease can completely eradicate the whole population. If you have a diverse enough gene pool there is a big chance any change will not affect every individual animal and thus survival of the species is more likely. Likewise, diversity of ideas and approaches to life in the human population will help us solve future problems that we can't predict. An idea that seems crazy Today can be a life saver Tomorrow.
Finally, unchallenged ideas can go stale. Arguments open up new ways of thinking about problems and help fine tune your position.
Therefore, it is beneficial for us all to uphold diversity of opinion in society. When you're arguing always remember this counterintuitive thought:
On the long term you indirectly benefit from the opposing views of your adversary.