Persuasive speech is as old and reputable as factual, informative speech. It occupies, in fact, a far larger domain in everyday conduct. A good two thirds of speech that goes on is of a persuasive character. Most politicians' speech is persuasive. Most artistic speech is persuasive.
Much religious speech is persuasive.
You are then in good or bad company, if you're in the business of persuasive speech. And the rhetorical devices that advertisers use are essentially of the same sort as used by politicians, religious leaders and artists. They were ennobled both by Greek commentators and Roman commentators talking about different sorts of speech. So advertisers shouldn't pretend that advertising should be like scientific reports. It should glory in the fact that advertising is of a rhetorical character and should explain that this is part of what much of speech in our society is about.