If this was the case, it would be near-impossible to write HTML by hand. And if you're writing HTML with a tool (React, HAML etc.), the tool could be doing HTML escaping correctly instead. This isn't an issue with HTML, it's an issue with human error.
All security issues are due to human error. Those are solved by building better tools.
> If this was the case, it would be near-impossible to write HTML by hand.
If, besides the text form, there would be a well-defined length-prefixed binary representation, we could simply compile HTML to binary-HTML, which would immediately made the web not only safer, but also much more efficient (it's scary if you think just how much parsing and reparsing goes on when displaying a web page).
My point is that there's nothing wrong with HTML. HTML isn't a tool, it's a format for storing and transmitting hypertext. If you're using React or HAML or any of the other HTML-generating tools, you're effectively immune from XSS. I'm putting forth that developers aren't using effective tools (shame on every templating engine that doesn't escape by default), and that calling the web as a platform bad is a bit nonsensical. It's like saying "folks are writing asm by hand and their code has security issues, therefore x86_64 is insecure".
However, no such tool exists. I think there's a deeper issue here: the sheer number of ways you can generate XSS alone, even ignoring the other exploit types, is far beyond what any tool is capable of stopping. Look at one of the XSS holes found by Homakov that I linked to from my article:
http://sakurity.com/blog/2015/06/25/puzzle2.html
The XSS occurs on this line of JavaScript, not HTML:
$.get(location.pathname+'?something')
Show me the tool that would have avoided that type of exploit, without already knowing about it and having some incredibly specific hardcoded static analysis rule.
When I argue that the web is unsafe by design, it's because cases like that aren't rare, they're common. To paraphrase Veekun, scratch the surface of web security and you'll find yourself in a bottomless downward spiral, uncovering more and more horrifying trivia.