Oh god, where is the validity?

There was a discussion on validity. Rather, the point was that IT development is on (and there is no need for indignant sighs here!), In Ukraine, I say, behind the entire planet. But they somehow quickly forgot about it, and the question turned into another plane.

Validity or not valid? That is the question.

Why is this fanatical desire for a valid code? What are its practical advantages, except that it is basically a standard?
')
Here "Habra" is not valid , for example. And what, let us together cease to hang out here. She's not valid!

In short, users need to think, not about the image. The user will be pleased - will be the image.

Update
Thanks to everyone who was noted in the comments. Intelligible explanations are only for the benefit. To me :)

True, I did not mean that the invalid "Habra" is bad. But that's another story.

Update2
A kind of continuation of the discussion novikov.habrahabr.ru/blog/5404.html .