Specialization vs. diversification

In class today, someone asked why more companies are not diversifying their products and services. As a consumer, do we really want them to? When companies operate under a comparative advantage, which is the ability of a firm to produce a particular good at a lower opportunity cost than any other firm, (http://en.wikipedia.org/wiki/Comparative_advantage)consumers get the more for our money. Specialization maintains a certain balance in the market. Under specialization, ideally each firm has something or can do something better and more efficiently than the other, so in turn they are dependent on one another. Here is an example: a produce man depends on fertilizer and pesticide companies and vice-versa. This allows many different firms to make a place for themselves which in turn gives way for more jobs.
On the other hand, let’s say companies begin to efficiently diversify their products and services. They become less dependent on other companies, with no need for these companies they go out of business and people loose their jobs. Efficiently diverse firms are more beneficial to themselves than to consumers or the market as a whole. When companies become independent, competition decreases. This leaves room for more monopolies, and then the consumer suffers due to high prices and a lack of variety. We should consider ourselves lucky that the majority of firms have not found a way to efficiently diversify their business, and that they focus more on specialization.