If you go by the American-style "absolute freedom" mantra, I get where you're coming from.
On the other hand, casting a vote doesn't mean CHOOSING a candidate. It means that you can cast a BLANK vote. And that, in and of itself is an extremely important thing. It shows that you are NOT okay with either candidates, and forces them to actually adjust their agendas to suit the "public will", instead of falling back to what I believe is commonly called in the US as "ratfucking", aggressive districting, and voter disenfranchisement, which means they literally only care about getting enough voters to pass.
As for the doability, it's already done in Australia. Pretty successful, and basically and national holiday celebrated like 4th of july in the US.