Voting is the one time most citizens take to express their opinion. While I wish they would express it much more often, many don't. If they don't vote for the candidate whose positions they most closely agree with, we never learn what voters really think. Strategic voting to avoiding spoiling attempts to convince voters to vote based on who they want to lose, not who they want to win, or what policies they think are best. This is not democracy in action.
Third parties have along history of being the engine of ideas in the United States.
Many programs and polices now taken for granted were initiated by third parties. While I do not want the adoption of Green Party policies by a major political party to be our primary legacy, if that happens, our efforts will still have been justified. And by basing our strategy on a plan to become a major party, we will have the largest positive impact on policy. And having our issues usurped is not necessarily the most likely result. Ongoing success by the Green Party in New Mexico has made the adoption of Instant Runoff Voting likely it missed passage in the New Mexico state Senate by only one vote last year.