Rhetoric gained negative effect when used by politicians, because people began to wonder if they really meant what they said, and whether they would keep up with their words (as in political campaigns, for example).
But in principle, rhetoric could be really positive and it was formed over the centuries, and viewed as the 'art of persuade others'.
The rhetoric was born in the 5th century BC in Sicily, and was introduced to Athens by the sophists, and used in political and judicial circles of ancient Greece.
Nowadays rhetoric is the study of writing, and academic writing divides it into rhetorical modes, considering nine the most common.