:Reliable sources are for factual claims, not interpretations. Reliable sources say Beethoven's 9th is beautiful. Nonetheless, Wikipedia should not say Beethoven's 9th is beautiful. An encyclopedia doesn't interpret things. In this case, the difference between adding "by some" or not is that without "by some" Wikipedia is stating as a fact that all Holocaust demnal is anti-Semitic, whereas if you add the "by some" we are making it clear that this is an interpretatation. Neither is very good. The proper way to present the idea is with some information about the prevalence of the interpretation as anti-Semitic. I doubt anybody has bothered to research it, so I doubt there is anything encyclopedic that can be said about it. This is really just a small case of the usual Wikipedia bullshit of people using the encyclopedia to promote their worldview. Whether it's an article on Jesus or Middle East politics, this community is full of hate-mongering ideologues who would rather shove their self-glorifying ideologies down the throat of the world than produce a fair and balanced enyclopedia that has has integrity. There is a reason that study of the reliability of Wikipedia that everybody likes to cite only looked at science articles.