How does user interface design relate to coding? Coding is easy. Unfortunately perfect knowledge of CSS specifications will not give you anything in this field.
The only valid CSS could break the UI. Invalid do nothing. Coding is nothing here. Coding skills are required but not enough.
I don’t get it. I’m not an expert in UI (please don’t mix UI and coding skills). It is true. But why can’t I have a strong opinion? Reasons may be different.
Even you have a great reason to support the ban of CSS.
As you said, it is based on imagination, not expert skills. So being an expert is not necessary.