Why is a fundamental investor suspicious about a required return estimated from the capital asset pricing model

Question:

Why is a fundamental investor suspicious about a required return estimated from the capital asset pricing model (CAPM)?

Capital Asset Pricing Model
The Capital Asset Pricing Model (CAPM) describes the relationship between systematic risk and expected return for assets, particularly stocks. The CAPM is a model for pricing an individual security or portfolio. For individual securities, we make use of the security market line (SML) and its...