Should we have Democratic Sacred Cows?

Across the Western Democratic, and Liberal-Democratic world the end of history has proven premature. Some of the foundational bedrocks of many western states have come under attack, freedom of press, religion, association, and even democracy itself from Turkey to the US there have been a number of challenges to those rights once viewed as unassailable.

This election in the US has seen several candidates challenge some of the other tenets of the basic post-war settlement like Free Trade, and NATO.

Which all raises the question of whether or not we should encourage or even accept such challenges? Should the US and democracies allow anti-Democratic to organize and head to the ballot box?

Is it required for Democracies to allow parties and politicians that reject a secular order, when one is enshrined in the Constitution? How about passing popular laws that serve to severely curtail the free press? Banning Political Parties from participating? What about when those parties seek to violently overthrow the government? Is it fair to ban them then?

Should those things be beyond reproach, never to be debated, a prerequisite for existing as a political entity in a free society? Or does making that a requirement prevent it from being a truly free society?

Some states and times have done so, Turkish banning of the Welfare Party while others have taken far more lax approaches allowing such forces to organize while relying on other means to ensure they never stripped away the basic freedoms which they agitated against. But what should our approach to those sacred cows once thought undeniable, but now often contested in various places be? Acceptance, Denial, or something else?