'Neither be the dupe nor victim' can be best understood as :

Read the passage given below and answer the question.

You seemed at first to take no notice of your school-fellows, or rather to set yourself against them because they were strangers they knew as little of you as you did of them; so that this would have been the reason for their keeping aloof from you which you would have felt as a hardship. Learn never to conceive a prejudice against others because you know nothing of them. It is bad reasoning and makes enemies of half the world. Do not think ill of them till they behave ill to you; and then strive to avoid the faults which you see in them. This will disarm their hostility sooner than pique or resentment or complaint. I thought you were disposed to criticize the dress of some of the boys as not so good as your own. Never despise any one for anything that he cannot help least of all, for his poverty. I would wish you to keep up appearances yourself as a defence against the idle sneers of the world, but I would not have you value yourself upon them. I hope you will neither be the dupe nor victim of vulgar prejudices. Instead of saying above "Never despise anyone for anything that he cannot help," I might have said, "Never despise anyone at all"; for contempt implies a triumph over and pleasure in the ill of another. It means that you are glad and congratulate yourself on their failings or misfortunes.