Print designer would have to know paper materials/textures/printing press to design well
I don't think this translates to
If s/he designs for the web, s/he then would have to be able to understand/write some code to design well for the web.
You're equating "knowledge" with "ability", and you aren't respecting the very large gap between the two. Expecting a web designer to code is akin to expecting a print designer having the knowledge and foresight to determine paper size and gang-up print pages for the printer so they can just start printing.
When I was working in print production, however, we had jobs where designers would try to do this as a way of "helping out", but this was rarely if ever helpful and almost always required a lot of extra work to fix. The production team determines the best way to print, not the designer. The production team knows what size of substrate they're using, not the designer. A designer is best limited to understanding the complexities associated with the production of a given product as a way of influencing their design, but in no way should they be expected to actually do the work that another discipline has far more experience with.
I don't think this translates to
You're equating "knowledge" with "ability", and you aren't respecting the very large gap between the two. Expecting a web designer to code is akin to expecting a print designer having the knowledge and foresight to determine paper size and gang-up print pages for the printer so they can just start printing.
When I was working in print production, however, we had jobs where designers would try to do this as a way of "helping out", but this was rarely if ever helpful and almost always required a lot of extra work to fix. The production team determines the best way to print, not the designer. The production team knows what size of substrate they're using, not the designer. A designer is best limited to understanding the complexities associated with the production of a given product as a way of influencing their design, but in no way should they be expected to actually do the work that another discipline has far more experience with.