NNous sommes des animaux vs Nous sommes animaux
Why do you have to use de + les in this sentence? What would be the meaning of Nous sommmes animaux without des?
In the sentence "Nous sommes des animaux", the word "animaux" is a noun, masculine, plural. In English, it means "We are (some) animals". In the sentence you suggest, "Nous sommes animaux", the word "animaux" would be an adjective, masculine, plural. This adjective is rarely used, and it is mostly used in this kind of expressions: "l'échelle animale = the evolutionary ladder". Thus, the sentence "Nous sommes animaux" (without "des") would have no relevant meaning, both in French and English.
In French, all nouns need an article or an adjective except in very limited circumstances. Animal is not one those exceptions. Therefore it needs an adjective or article.
In this sentence there is no adjective. Thus you need to have an article. The only question is which article.
Remy discusses that in this thread.