Exerting political power
Given the decrepit state of what some of us still consider our democracy, it is not surprising that many citizens no longer believe that it is worth their while to vote in elections. Democrats and Republicans sometimes appear as two faces of the same plugged nickel. Third-party candidates, with some exceptions, have such difficulty in capturing the public's attention and garnering political support, that their battles to win elections often appear quixotic.
Boycotting an election does send a message of sorts, but it is not the type of message you really want to send. By not voting, you may indicate your lack of trust in our political system, but you are also saying that you can be disregarded; that no one needs to contend with you or seek to please you; that the "Powers That Shouldn't Be" can walk all over you, can wipe the floor with you.
The higher the voter turnout, the harder it can be for the people who may try to rig the election to do carry out their nefarious purpose. And if they do succeed, the harder it can be for them to cover up their actions. Some people may still believe that the Democratic Presidential Primaries of 2016 were not rigged against Sen. Bernie Sanders, but millions of Americans cannot help but know the contrary: the fraud was so blatant and obvious that it was surely one of the factors that led to the Clinton loss in the general election.
So GPMI members should never be hesitant about showing up at the polls on Election Day. Michigan's primary system gives you the opportunity to influence the selection of major party candidates, and the general election gives you the chance to exert your Green values, most especially by supporting Green or Green-endorsed candidates when you can.