Search engine optimization ( SEO ) is not considered spam by Google. The statement on this account is given by Matt Cutts head of Google’s webspam 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 that generates webspam or there are many SEO companies that use spam method to improve ranking But Good SEO helps people  in finding on search engine what they need

Here is a video of Matt Cutt where he said SEO is not a Spam