Sentence:  That a writer who is gay cannot be serious is a common professional illusion , sedulously fostered by all too many academics who mistakenly believe that their frivolous efforts should be taken seriously because they are expressed with that dreary solemnity which <WSD>is</WSD> the only mode of expression their authors are capable of . 
Meaning of the word marked with <WSD> tags:  be identical to; be someone or something