Why must shares be paid up in money or money's worth?

The requirement for shares to be paid up in money or money's worth primarily aims to protect the company's asset value. When shareholders contribute capital, either in cash or equivalent assets, they are providing the company with resources that can be used for its operations, investments, and growth. This capitalization is crucial as it establishes the financial foundation of the business and ensures that the company has actual assets backing its shares.

By requiring shares to be paid up in tangible value, the company ensures that the investment made by shareholders is valid and contributes to the overall financial stability of the organization. This also serves to prevent situations where shares could be issued without real underlying value, which could lead to financial instability and shareholder disputes down the line.

In the context of the other options, while ensuring fair trading practices and complying with financial regulations are important considerations, they do not directly address the foundational aspect of maintaining the company's asset value. Additionally, providing equity to shareholders is a result of proper capital structure but is not the primary reason shares must be fully paid in real value. Thus, protecting the company's asset value stands out as the most relevant rationale.