The problem is that you can demonstrably point out objective flaws with using wheelbarrows and bags of concrete (or I assume you can - I know nothing about pouring foundations).

With the cult of semantic HTML, the flaws in using class names to describe presentation are almost always not explained beyond some vague notion of "correctness", and possibly an example that bears to relation to reality when you take into account that almost all HTML is being generated by some sort of templating engine anyway.