He can voice that opinion because (a) he is correct, the sources only say he was Jewish, but not that this is relevant to this writings on racism ; (b) it is established Wikipedia policy that we don't call out a person's background - be it racial, religious or ethnic or other - unless it is pertinent to the topic as evidenced by reliable sources making that connection; and (c) this is the consensus on this page - 3 editors have told you that what you are proposing is not acceptable, it is time for you to stop edit warring it back into the article.