The spam messages I've seen have almost without exception advertised stuff that's worthless, deceptive, and partly or entirely fraudulent. It's all stuff that's too cruddy to be worth advertising in any medium where they'd actually have to pay the cost of the ads. Also, since the cost of spamming is so low, there's no point in targeting your ads, when for the same low price you can send the ads to everyone, increasing the noise level the rest of us have to deal with. Spam software invariably comes with a list of names falsely claimed to be of people who've said they want to receive ads, but actually consisting of unwilling victims culled at random from usenet or mailing lists. Spam software often promises to run on a provider's system in a way designed to be hard for the provider to detect so they can't tell what the spammer is doing.
Spams invariably say they'll remove names on request, but they almost never do.
Spammers know that people don't want to hear from them, and generally put fake return addresses on their messages so that they don't have to bear the cost of receiving responses from people to whom they've send messages. I could go on, but you get the idea. It's hard to think of another line of business where the general ethical level is so low. It might be illegal. Some kinds of spam are illegal in some countries on the Internet.