From my perspective (and without reading the book), what Ralph Nader is advocating for isn't enough in the present day.
Clearly, the change we need in America is systemic - getting an establishment neoliberal (who is likely to run as a moderate) to budge on specific policy changes is insufficient action to change our trajectory as a country.
I believe that it is in the spirit of democracy to encourage others to vote however they want to - that includes forming voting blocs and doing exactly what you are shedding light to.
I feel that in a democracy, it is desirable for candidates to actively be making attempts to appeal to potential voters and actively attempting to represent their interests; instead of running on effectively maintaining the broken status quo - with minor changes.