English differs from some other languages in its usage of "the" (the definite article).
English does not use "the" before general categories. "The" is only used with nouns that can explicitly enumerated.
Omit definite article:
General category, you don't have specific individuals in mind:
Web designers are smart people
Still a general category; it only has an extra specifier. You still don't have specific individuals in mind:
Web designers from Google are highly motivated
Include definite article:
Now you have specific individuals in mind; you can list them out by name:
The web designers went out to lunch (that is, Alice, Bob, and Carol)
Contrast with Spanish
Spanish for example, uses the definite article with categories, unlike English.
If you enter "Programmers are smart" into Google translate from English to Spanish, you'll get:
Los programadores son inteligentes
Where "los" is the definite article.
More Info on categories
There are cases when you'd use the definite article with categories, but only indirectly. For example, in this case, "the" is modifying "subject" and not the category.
The subject of web designers intrigues me
More here: https://en.wikipedia.org/wiki/English_articles#Use_of_articles