Trying to fear people into voting for a candidate is stupid — it’s also stupid to blame Stein voters for a potential Clinton loss because Stein is polling at 2–3~%, so the votes she receives wouldn’t save Clinton in any significant way.
Dems have been saying these types of things about every republican presidential nominee since GHBW’s re-election year. It’s frankly embarrassing, as a dem myself, because using fear as a motivator to vote is what the GOP does. Dems also never want to take credit for their obvious faults — Dems are still whining about Nader near 2 decades later instead of Gore’s atrocious campaign (HE LOST HIS HOME STATE FOR CRYING OUT LOUD!).
You know what does work and would get people out to vote? Offering single-payer (or a public option) healthcare (not insurance, healthcare), offering free college tuition to public universities or student loan forgiveness, not engaging in more wars, not aligning yourself with Neocons, ending military aid to countries like Saudi Arabia, UAE, and Israel, actually ending fracking and pouring billions of dollars into solar and wind energy, and generally just acting like you give a damn about the country not just your mega donors. The first two things aren’t even radical, we’re one of the only industrialized countries that does not have nationalized healthcare and free (or cheap) university tuition.
If Hillary Clinton loses the election, it won’t be because of Stein voters, Gary Johnson voters, or millennials — it will be all on Hillary Clinton.