Here is what Wicksteed says:

“He is exactly in the position of a man who is playing a game of chess or cricket. He is considering nothing except his game. It would be absurd to call a man selfish for protecting his king in a game of chess, or to say that he was actuated by purely egoistic motives in so doing. It would be equally absurd to call a cricketer selfish for protecting his wicket, or to say that in making runs he was actuated by egoistic motives qualified by a secondary concern for his eleven. The fact is that he has no conscious motive whatever, and is wholly intent on the complex feat of taking the ball. If you want to know whether he is selfish or unselfish you must consider the whole organization of his life, the place which chess-playing or cricket takes in it, and the alternatives which they open or close. At the moment the categories of egoism and altruism are irrelevant.”

“[...] Once more, then, if ego and tu are engaged in any transaction, whether egoism or altruism furnishes my inspiring motive, or whether my thoughts at the moment are wholly impersonal, the economic nature of the action on my side remains undisturbed. It is only when tuism to some degree actuates my conduct that it ceases to be wholly economic. It is idle, therefore, to consider “egoism” as a characteristic mark of the economic life.”*

That it is to say that the rules of the game determine how people act in exchange. If you have to protect your king, you protect your king. This does not make you a selfish person. Similarly, if you have to get the best trade (this seems to be the rule of the exchange game), you behave accordingly. This does not make you a selfish person.

Nevertheless, Wicksteed characterizes the exchange game as a game that requires/imposes selfish behavior. Thus, while it is true that it is wrong to label players of this game as ‘selfish’, we may be allowed to label the game as a selfish game and “consider “egoism” as a characteristic mark of the economic life”.

Kirzner argues that ” Wicksteed’s rejection of egoism allowed him to include under “one’s own purposes” every conceivable interest except the interest in the person with whom one is dealing.”** Yet he also argues that “There is undoubtedly an element of artificiality, albeit ingenious artificiality, in this exception. If “one’s own purposes” are wide enough to include concern for the support of charitable institutions, they are surely able to include an interest in the welfare of the person with whom one is dealing. Despite the skillfulness and persuasive beauty of Wicksteed’s prose, it remains difficult to see the boundary line as other than the result of a quite arbitrary piece of surgery on the whole of commercial activity”**

I also think that economics can be compatible with altruistic behavior, but I doubt that Wicksteed’s defense is the best defense of this idea.

* http://www.econlib.org/library/Wicksteed/wkCS5.html
**http://www.econlib.org/LIBRARY/NPDBooks/Kirzner/krzPV3.html

I think it can’t be denied that the model of “economic man” has been frequently resorted to by economists. It’s certainly one of the simplest possible models to analyze.

Perhaps you should reply to your fellow social scientists that they should help us discover better models for the content of preferences, rather than merely sniping at admittedly deficient (though perhaps adequate for many purposes) models.

(And to be extra clear, non-tuism refers to the exchange partner's well-being only, not the well-being of third parties.)

Of course, modern economics is not committed to non-tuism.