votes third party

No not like that

Seriously though, I think it's important to confront and admit that voting for the lesser evil does legitimize the evil they do, even if the greater evil does it worse. Because critically digesting both that fact alongside the fact that voting for the lesser evil really does result in better outcomes for society is what will actually get the hesitant on board with going and doing it. If you try to dismiss or handwave that fact, you are dismissing and handwaving the very real concerns of the disillusioned non-participants. Acknowledging the dissonance is far better.

I think it's also important to point out that while direct action and social organizing are the most effective things things you can do to change society, they are incredibly time consuming while voting usually takes 5 - 30 minutes. And if you're actually interested in the former, there's little to no excuse to avoid the latter.

Just whatever you do, don't shame people for being disillusioned. That makes people really dig in their heels.