To be an ethical SEO and Webmaster is easy. Just observe some simple rules. First and most important: don't spam. Don't spam people with low quality content and pages purely for the idea of advertisement. Those sites are so annoying that almost all the visitors will close the window right away. Provide people with useful and interesting content. If they like your site they will stay longer.
Also don't spam the social bookmark sites and forums solely for the purpose of traffic and link building. Share high quality articles and make people enjoy reading them.
Captcha ... Have you tried to register on a page full of advertisement, with an annoying, unreadable captcha? Most of the seo directories are made this way. Submit form spread all over the page, with an advertisement with the same font between, and a captcha that fails two-three times. Don't do this. Even if it makes few impressions people will not ever return to you.
All this is not for a bad or good practice in search engine optimization. It is for pure human behavior. And looking from a distance, all the web sites and services that have succeeded in making really good money have granted the public something useful.