[Gettersaga]

I don't understand the meaning of a part of sentence when it is seen in the global context of the previous part ... Nagoyankee, please tell me what it could mean.
First of all I'll tell you the meaning of the previous part as I understood it(where we were arrived to see it).
" ... unfortunately I am crouched inside the air raid shelter refuge and on my knees is opened only an illustrated book for children. I, depending only on this illustrated book,"
論断せざるを得ないである
論断 is "conclusion" but "I have no other choice that to conclude", is it possible?
It seems to me that there is something that I don't understand. I'm wondering if Dazai wants to tell the reader that he must conclude this matter about oni, kisai and bungaku no oni. If it isn't so, what does that " 論断せざるを得ないである" mean?