George Orwell said: "In practice nobody cares whether work is useful or useless, productive or parasitic; the sole thing demanded is that it shall be profitable." What does he mean by that? And how could I argue the view using evidence from the text?

Orwell writes that, in the eyes of society, the only thing that matters about work is that it be profitable. He says this in order to make a sympathetic case for the life of a beggar. Orwell states that people accuse beggars of not working. Orwell then asks, what is work? He says that beggars actually do work hard and likens their work to work other people do. Why can a person be arrested for begging, he asks, but not for drawing on the sidewalk with a piece of chalk and hoping someone tosses him some money in return? Orwell goes on to say that

A navvy works by swinging a pick. An accountant works by adding up figures. A beggar works by standing out of doors in all weathers and getting varicose veins, chronic bronchitis, etc.

Orwell does then admit that the beggar's work is useless. But Orwell asks, how many people in reputable professions are doing anything useful? For example, he says that a beggar is more honest than a person who sells patent medicines. He notes that the beggar may be a parasite, but he is a harmless one.
What separates a beggar from any other businessman is that the beggar's business doesn't make much money. It's not the fact of begging that makes him despised, but the fact that he doesn't make a respectable income from it. As Orwell puts it:

A beggar, looked at realistically, is simply a businessman, getting his living, like other businessmen, in the way that comes to hand. He has not, more than most modern people, sold his honour; he has merely made the mistake of choosing a trade at which it is impossible to grow rich.