Why do words with negative connotations have negative connotations?

In some cases like the word vice, the negative connotation stems from a direct definition of the word (vice means wicked, but another definition is 'a substitute for' so 'vice president'). In other cases, word may be used in a culture to identify a group or individual that is portrayed negatively, thus modifying the inherent definition of the word to better portray how society thinks of the word.