I think you're falling into the trap of assuming that all votes that go to Stein would otherwise go to the democrats, instead of just not showing up or voting at all. There is no reason to believe that Green party voters would vote democrat if not for the Greens on the ballot.

The only people I know who are voting green in this or any election would either a) otherwise vote democrat or b) not vote at all and are EXPLICITLY being contrarian in an attempt to "punish" dems for being insufficiently/the "wrong kind" of leftist.