Search Engine Optimization is of course an ethical practice. If you don't do SEO, how will you gain visibility on search engines and gain traffic. If you do not have traffic, how will you earn from your website. SEO is of course ethical, however, what kind of SEO you are doing is important. For instance, SEO is broadly classified as Black Hat SEO and White Hat SEO. White Hat SEO is a good way to gain higher rank on search engines where as Black Hat SEO is an unethical way to manipulate search engine ranking. Some of the unethical SEO, or Black Hat SEO are: using link farm to create backlinks, using link wheel or private blog network, using wrong keywords, using bots to create automated backlinks, using social exchange to generate social signals, using wrong meta descriptions and meta tags etc.