Should web designers do their own HTML/CSS?

After reading this post I wanted to post a comment, but as I began writing it sort of grew into a post by itself, so here is my response:

I think web designers should know how to build with (X)HTML/CSS but no more than an architect knows how to build with formworks and concrete. Designers think websites while coders build those websites just like architects think buildings while masons construct those buildings.

In circumstances, it is an advantage to know little of the tech details because that innocence allows for greater revolutionary thinking. Many designers who also code themselves restrict unconsciously their designs to what they can code – or to that which won’t mean a hard work to get it coded. I speak for my own experience.

At the same time, I think that knowing to code does not make a designer, just like knowing how to use concrete or formworks does not make you an architect. There are coders out there who call themselves “web designers”, but have no clue about design, about web principles, about proportion, space, hierarchy, order, balance, contrast, usability, consistency and all which makes great design great.

So while it is true that a designer who does not know HTML/CSS cannot call himself a web designer, the contrary is also true: a person who knows HTML/CSS cannot call himself a web designer if he has no formation whatsoever in design. And, by the way, print design formation helps much because much of the best principles and practices in design are universal and apply to both the offline and online spheres.

By the way, where is Flash in this debate? Or a Flash web designer is not a web designer?