The Op asked us if WC is necessary and why. Why is it thier job to carry the burden of proof for our answers?
As for the benefit of assumption all you are saying is that we the majority have the benefit of one of the worst ways to make a decision known to man.
He may have asked, but by his statements it is obvious that he believes they are NOT important. Since they are arguing against the general assumption, one that has been slowly modified and built upon though time, they carry the burden to prove that the generally accepted idea is not right.
As for your second claim, that the majority having the benefit of the doubt rather than the minority being 'one of the worst ways to make a decision known to man', I beg to differ.
A few examples. The majority believes that murder is a bad thing. Should we say that perhaps those that believe murder is a good thing have the benefit of the doubt?
The majority holds that beating a child is a bad thing, while a minority might claim that it is their right as a parent. Should we have to prove to them that child abuse is a bad thing, or should they have to prove that it is a good thing?
The majority of people would say that psychology is an important scientific field, one that helps many people. But should we have to prove all this to Tom Cruise with page after page of facts? I would rather see his evidence that it is a sham!
For a long time, the accepted conclusion about our Earth was that it was flat, an was the center of the universe. However, evidence was provided by scientists that proved time and time again that it was not. The scientific community fulfilled it's burden of proof against the accepted conclusion.
The majority of people, as supported by this poll, believe that water changes should be performed regularly, and are important. A huge amount of anecdotal data also supports this conclusion. The OP, feels that they are not, but provides no strong evidence to support his claims.