Search engine optimization ( SEO ) is not considered a spam by Google. The statement on this account is given by Matt Cutts head of the Google’s web spam fighting team.
Matt Says “We don’t consider SEO to be spam,” and added that SEO is “a valid way to help people find what they’re looking for via search engines.”
He agrees that there are many Black hat SEO which generate web spam or there are many SEO companies which uses spam method to improve ranking But Good SEO helps people in finding on search engine what they need
Here is video of Matt Cutt where he said SEO is not a Spam