The way the criticism is presented is childish. W3Schools is the most accessible introduction to web technologies that I've ever seen. It assumes absolutely zero knowledge. When you're literally just starting out, this is a big deal. You don't give a damn about standards, you just want to create and make cool things to show to your friends. It's a jumping off place. Criticism of W3Schools as a reference I have no problem with; clearly there are extensive inaccuracies, but telling beginners to learn HTML/CSS/JS from MDC is equivalent to telling them to RTFM.