I'm with Netscape 4 on this one. To my mind it's conceptually no different from a frame -- you need the file to display the page, the file isn't there -- man, you got a broken page. And, frankly, as a webmaster I'd want to know ten minutes before immediately, if the page I uploaded is broken.
I know that there are a lot of webmasters out there who really don't "know" html in any grammatical sense, who sort of schlep stuff together -- just like they were hacking a brochure in MS-Word -- and who really can't understand computer-generated errors, let alone figure out how to fix them. And the browsers don't want to be in the business of reporting errors, or of being seen as being too "picky" about common ones, so they try to do "something sensible" with them.
And you know what we get? A world in which every bleeding page has to be tested with every version of every common browser, because each one of them does something different -- sensible or accidental -- with this grammatically-incoherent stuff that should have been strangled before birth.
So a browser that immediately chokes on anything the least bit out-of-line with the most restrictive standard possible is ... what I most want (and really don't have) for all my own development work.