Why do some people find it unacceptable to use the term "animals" in a context where the word excludes humans?

Why do some people think that anyone who casually says something like "humans and animals" has to be both corrected and insulted? I mean, sure, humans technically are animals, but this is still just everyday language. There is a book called a dictionary that confirms that it is okay for common words to have more than one definition, based on the context in which they are used. Most importantly, just because someone casually uses everyday language does not automatically mean that they are some sort of scientific illiterate who does not consider humans to be animals. So how is this seriously any more ignorant than using the term "bugs" to describe terrestrial arthropods in general, when it technically refers only to a specific order of insects? I mean, sheesh!