Yes, because then you will work for what you want, and buy what you need.
There has to be assumptions behind every academic theory. This is appropriate for econ not because it always works, but because it generally works.
Self-interest is entirely appropriate for economics. The problems arise when: A) The interest of the selves in question becomes divorced from their actual physical needs (i.e. there's a good reason to hoard more than you need.) The Founding Fathers of the USA tried to keep this from happening by preventing fortunes from being passed from one generation to the next -- on the assumption that if you couldn't keep it 'in the family' when you died, you wouldn't be interested in obtaining more than you could use. See how long that lasted? And B) We substitute 'shareholder interest' (or any other form of collective interest) for self-interest -- as is the case with any publicly-traded corporation -- because there is no *reasonable limit* to shareholder interest. 'Shareholders' are not people, at least not as far as the corporation is concerned -- there is no point at which 'Shareholders' can be satisfied with their profit margin. Because the desire of 'shareholders' is never-ending, the drive for ever-greater profits is intense, and the purpose of LIMITING GREED TO MERE SELF-INTEREST (which is the actual effect of talking about the market in terms of self-interest) is lost.
Self interest does not constitute theft or coercion, it is simply a desire to satisfy your desires and fulfill your value preferences. You can pursue your self interest in a rational way(i.e. consideration of others and the resultant cooperation and exchange) or irrationally (theft, taxation, slavery, etc.).
Without taking into consideration other people, you do not create an equal environment and it would end quickly and horribly.
Not Always.... The tragedy of the commons can shade some light on it.