WB.SE needs to be 5 because we are such a multi-disciplinary stack
KeizerHarm already covers most of the reasons why 5 is good in his answer; so, I won't really go into repeating them, but for me the biggest reason why this is true of WB.SE is because WorldBuilding is multi-disciplinary: this makes bad close votes much more common here than in other SEs because we are more likely to vote to close when we do not understand the all of the fields of study that could be applied to a question.
You seeI've personally seen it all the timedozens of times: a question gets 3-4 downvotes really quickly because someone thinks it is opinion based until someone comments explaining why it is not. The it goes on to becoming a very active and well accepted answer without the question needing any revision at all.
For example, you may have a highly intelligent and reputable stack user who maybe specializes in astrophysics and chemistry will read a question and vote to close it as an opinion-based question being completelyonly because he is unaware of the mountains of research that someone with a background in anthropology and linguistics would be able to cite to give a definitively factual answer to the question well within the SE guide-lines.
And this is not a one way street either, a person coming from a soft science-science background will just as often vote to close because they do not understand just how advanced modern science really is. For example: a person may ask a So, hard-science questionquestions about nanobots or, laser weapons, and some people willstun beams are very likely VtC the questionto get a couple of down-votes just because they do not knoweveryone knows that nanobots and laser weaponsthese are real technologies that exist today.
By reducing to 3 votes, you make questions that are harder to answer much more likely to be closed as opinion based just because a couple of people do not understand the topic well enough to give an informed response.