This is a fallacy listed, "the fallacy fallacy", first column second row on the left with the symbol of a fractal.
.data {
font-size:11px;
font-family:Courier;
color: #555;
}
.magic {
color: royalBlue;
}
<p class="data magic">Magical data</p>
<p>Normal text with <span class="magic">magical <span class="data">data</span></span>.</p>
I've inherited .magic into .data without sacrificing the ability to use .magic and .data by itself. As long as you keep your CSS classes semantic and disperse them intelligently into the markup, it's really not an issue of making large scale changes with minimal effort. Of course, in practice, this isn't always the case, but I think adding more ways to inherit properties will increase complexity more than help write good styles.