You have unstated assumptions embedded in your post.
You are not taking a vote away from Obama when you vote for Stein. It is far more likely that Obama is actually taking votes away from Stein, as Green party supporters vote strategically, because their 2nd choice is better than their 3rd or 4th choice.
Until such time as any US state implements a ranked-choice voting system, you have no way of knowing whether the candidate receiving the vote is actually someone's first choice, or a strategic vote for the second-to-last choice.
First-past-the-post voting essentially means that the 2 major parties are always stealing away almost all the votes that would have otherwise been cast for lesser parties. So a vote for Stein is actually "refusing to let Democrats steal your Green vote". You can't steal it away from the Democrats, because it wasn't theirs to begin with.
You are not taking a vote away from Obama when you vote for Stein. It is far more likely that Obama is actually taking votes away from Stein, as Green party supporters vote strategically, because their 2nd choice is better than their 3rd or 4th choice.
Until such time as any US state implements a ranked-choice voting system, you have no way of knowing whether the candidate receiving the vote is actually someone's first choice, or a strategic vote for the second-to-last choice.
First-past-the-post voting essentially means that the 2 major parties are always stealing away almost all the votes that would have otherwise been cast for lesser parties. So a vote for Stein is actually "refusing to let Democrats steal your Green vote". You can't steal it away from the Democrats, because it wasn't theirs to begin with.