Why would you need the original HTML for dev tools to work? Maybe there are ones I've never seen but the ones I use are using the DOM rather than the original HTML string.
One case where you would View Source in addition to using Dev Tools is debugging how the browser is massaging your source HTML into the DOM, for example by inserting missing <tbody> elements. Validating your HTML mostly addresses this (I'm actually not sure about the <tbody> example, I would hope the validator at least issues a warning), but isn't something you necessarily want or can do with, for example, user-uploaded HTML snippets.
True, though I guess using some HTML validation could improve that. Not sure if <tbody> is mandatory but I think I've seen some tool complain about its absence.
I showed a few people who have no idea about programming whatsoever how to hack websites to download .mp4 or .mp3 from source code of the website. How would you show them that using DOM...
Right but then you're talking about viewing the HTML source right? In other words "View Source." I'm asking why dev tools would need access to the original source and not the DOM. It doesn't make sense to save the original source in memory to me once it's been parsed.
One case where you would View Source in addition to using Dev Tools is debugging how the browser is massaging your source HTML into the DOM, for example by inserting missing <tbody> elements. Validating your HTML mostly addresses this (I'm actually not sure about the <tbody> example, I would hope the validator at least issues a warning), but isn't something you necessarily want or can do with, for example, user-uploaded HTML snippets.