1. Inform the consumer that certain offering exists. If someone invents a new superior type of coffee maker, they should let people know that there's now an option to make their coffee in a better way. There's nothing unethical in that. Of course, you can invent something like cigarettes, which people would be better without, but most inventions aren't like that.
2. Inform consumer that certain provider exists. I.e. if you have 20 coffee maker vendors, all alike, then when a customer goes to buy a coffee maker, they would tend to choose one they heard something good about, thus brand promotion and celebrity endorsements. This _might_ be somewhat unethical if inferior product is promoted with superior ones available, but usually there is enough offerings of similar quality that this is pretty neutral. Sometimes also something good comes out of it when companies sponsor worthy causes to get attention.
3. Associate the offering in consumer's mind with something positive and desirable. This one may be the ethically questionable one, as usually the association is completely bogus and is not based on any actual qualities of the offering but only on unsubstantiated claims of the advertiser that consuming the offering makes the customer "a kind of person" they want themselves to be. This is the kind that gives advertising the bad rep. But most online ads are actually not of this kind - it's just much harder to make such kinds of ads as a small banner.