I kind of don't buy that argument. The web is not fundamentally different from other programming environments, say Python or Java. It might sometimes be practical to have a python interpreter accept syntactically invalid input because it kinda knows what you mean anyway, but most programming languages don't work that way because it makes things harder in the long run, and the benefits are pretty miniscule.

The problem is that this kind of philosophy is fundamentally incompatible with HTML5.

There was an attempt for a "strict-mode" HTML, it was XML, but it failed (on the web) for various reasons (including IE). HTML5 specifies the exact behavior of what every browser must do upon encountering tag-soup, which is useful because real-world HTML has been tag-soup for a very long time.

I guess the strictest thing you can do is to die upon encountering "validation errors", but I don't think this would help much to simplify your job. (Maybe you can drop the adoption agency?) But now your parser chokes on a lot of websites - likely on hand-written HTML, which has a greater potential for validation errors but also typically simpler layout.

And HTML parsing is still the easy part of writing a browser! Layout is much harder to do, partly because layout is hard, but also because it's under-specified. Implement "undefined behavior" in a way that other browsers don't, and your browser won't work on a lot of pages.

(There have been improvements, but HTML is still miles ahead. e.g. CSS 2 has no automatic table layout algorithm, and AFAICT the CSS 3 version is still "not yet ready for implementation".)

Why would you want a web browser which can't open Facebook, X, or half of the other top websites?

And why would they bother to "fix" their websites when they work fine in Chrome, Edge and Firefox, but not in your very unpopular but super-strict browser?

> The web is not fundamentally different from other programming environments, say Python or Java

To me what makes the web completely different from any programming environment is the very blurry line separating code from data. The very same web page can produce totally different code two hours later just because of a few new articles with links, graphics, media and advertising. The web is that place where data is also code and code is also data; this must come at a price.

I think of the web like I think about Windows. Decades of backwards compatibility. Dubious choices that get dragged along because it is useful for people who can't or won't let go of stuff that works for them. It's a for better or for worse situation.