Numerous accessibility issues here. Many of these examples can't be operated by a keyboard, for example. "CSS only" is not a virtue if it comes at the cost (as it always does) of needlessly excluding people from the web.
All of these are fairly simple show and hide interactions that are easier to use, build and maintain when done with javascript, with all the content shown if JS is turned off, not fully loaded or broken.
Of course for accordion in particular it would be better if the pure HTML solution of using <details> and <summary> elements was supported in all browsers. They're already in Chrome and Safari and will come out from behind a flag in the next Firefox version. A polyfill for IE etc. can bridge the gap.
How many sites using Meyer's reset didn't add focus styles to links? Even with the comment /* remember to define focus styles! */
It's not the fault of the original developer but it certainly helps to have more robust examples.
I'm not saying your wrong, or that you are arguing against non-js browsers, just a funny twist.
Blind users can't opt to see.