Final answer:
Dreams might be referred to as 'sea foam' by serious-minded people to illustrate their ephemeral and insubstantial nature, which contrasts with Freud's belief in their deeper significance.
Step-by-step explanation:
The question about why some "serious-minded" people describe dreams as "sea foam" does not have a direct answer within the provided passages. However, one might infer that dreams are likened to sea foam because they are considered ethereal, transient, and without substance—qualities that could be ascribed to dreams from a skeptical viewpoint. Dreams are fleeting and often leave little trace, much like sea foam that appears and disappears on the edge of the sea. This view contrasts with Freud's perspective, which suggests that dreams contain meaningful insights into the unconscious mind.