I'm not sure whether SEO is unethical or not, to be honest.... the desire to appear within the top listings is fair enough... attempting to ensure that your site is their is only natural. If this requires optimisation, then fine.
What I beleive to be unethical is the methods by which some/most/all the SE work.
The rating of a site based upon content -- this is good, fair and sensible!
The rating of a site when it utilises graphics, a facy menu (non-txt-flash/js/j), has many levels, contains video, audio, flash files, uses tables for layout, doesn't contain <HD> tages, has a frontwelcome/home page with little content... not good, unfair and completely pout of date!
If I make a WS that is simply made of sole html, with no graphics, tons of bland txt, use bland txt links, has a huge <HD1> tage for the page title, a <HD2> for Section titles and <HD3> tags for sub-section titles, I place the words from my hdr, page/section/subsection titles as keywords and phrases... I can almost gaurentee being in the top three on almost all SE.
THATS NOT WEB DESIGN.
Yet thats the best way to get to the top without paying for it!
mentioning paying... now, depending on what you pay for raises ethics!
Some literally optimise your site... better Kwords+phrases, ensuring proper structure etc. This is good.
Placing links onlink indexes solely created of SEO, placing ads everywhere, this is not good!