[dimal]

Perhaps the term "semantic" is overloaded, but there are good reasons why presentational classnames are bad, even though users don't care and machines don't care. Your fellow developers should care. When done well, semantic markup is much easier to maintain and reason about. There's far less duplicated template logic and design changes are much easier because it's easier to understand where your changes will have an effect. The generated CSS might be slightly heavier, but possibly not. Poorly architected CSS tends to get very bloated and heavy very quickly. And there are better preprocessors like Sass or Stylus give you more options for keeping you generated CSS to a minimum. Less is really the worst preprocessor out there.

Every non-semantic bootstrap site I've seen has far more templates than would be necessary the templates only spit out minimal markup with classes that say what each element is instead of what it looks like.

But now we have tons of developers whose primary skill is backend development that are able to mash together a reasonable looking site without understanding how to create maintainable front end code. When the design changes, they just keep piling on more markup and more classes. This works for a while, but as designs get iteratively tweaked and changed, and kludges pile on top of kludges, the markup and CSS become a huge tangled mess. Making changes can have unpredictable effects on other parts of the site.

And then the back end developers throw up their hands and say, "CSS is stupid." But users don't care if the code is a mess, right? Machines don't care either. But the front end dev -- the one who's tasked with getting the new design to work without breaking anything else on the site -- he cares. And he's gonna have a bad time.