I think I get your point, but I'd say that first, not everyone always feels like they are voting for the lesser of two evils. For example, my take on the upcoming election s that Hillary represents the 'establishment' but so did Obama, and I thought he did a fine job, and I think Clinton will do fine as well, and on the other hand I view Donald Trump as an absolutely distructive force who could unintentionally light the system on fire, and because I like the system more than no system, I view this potencial burning down of the system as an unadulterated bad thing.

Secondly, there are three hundred mill on people in this country, if even a violent minority wanted to bring the government down, they could. Our country has seen very low levels of political violence historicly.
This is because most people dig our democrassy most of the time imo. For example, while congresses approval ratings are in the gutter, people approve of their own congressmans performance.