Diversity
I do believe that diversity is an important Professionalism skill. This is because, If you can only do one thing, and there are a lot of people who can do that one thing, then your chances of doing it for a living decrease. But if you can do a few things really well, then you should be fine. Although you probably can’t do everything perfectly, there are some extreme cases, it still helps to know other skills and have other abilities.
Just think of what the world would be like without diversity! How boring and monotonous everything would be… There would be no creativity or inspiration, because everything would be about the same. Diversity cures a lot of these issues. While creating very few, a problem that I can think of is people being unable to accept the diverse workforce, and just unwilling to work/do anything different. But, while there are still some people, I think that most of the workforce expects some degree of diversity between people, even in very a specialized area, like carpeting.
But as this is so supposed to tie into Web Design, If a person, who is a very good programmer, knows a bit about graphic design, then he can do his job a little bit better as he takes some different perspectives while he is programming.