>Because if you don't require evidence proportional to the claim, your world view can end up including any and all beliefs, which is neither interesting nor useful.
This is a reasonable approach, and probably the best universal algorithm we can choose, if we are forced to choose a single universal algorithm. Still it is clearly imperfect, limiting, and guaranteed to lead to false beliefs at some point.
The fact remains, by chance alone, that there are many important things that happened for which we do not have overwhelming evidence to support. Take all such events that have occurred in our history. Let us throw out claims made by individuals and only rely on claims made by groups of people. Let us assume that an overwhelming majority of these remaining cases are organized hoaxes. Even still, we are left with a number of cases where something happened for which we have no explanation, and no evidence, and no way of performing any further testing. These remaining events, by their nature, are guaranteed to be events that would cause a massive shift in world view for large percentages of humanity. The existence of aliens, God, and so on.
I find it somewhat silly that the two groups try to debate each other with any seriousness - those who have put their faith in God for which there is limited physical evidence, and those who have put their faith in the scientific method which requires physical evidence. The scientific method is a great tool, perhaps the greatest we have, but it is not perfect, and is guaranteed to lead us to mistaken beliefs at some point. Both sides are accepting some things as a matter of faith, whether they like it or not.