Is there a single-word alternative for "healthy dissent"?

Solution 1:

I would use debate:

Definition:

A discussion, as of a public question in an assembly, involving opposing viewpoints

Example:

A debate in the Senate on farm price supports

Or, discourse:

Definition:

A formal discussion of a subject in speech or writing, as a dissertation, treatise, sermon, etc.

Example:

The left needs to do two things if it wants to have an impact: give itself time, and change the discourse.

Solution 2:

contrariety

Definition:

the quality or state of being contrary

A couple of two word possibilities to consider could be contrary opinion or contrarian opinion.

http://www.dictionary.com/browse/contrarian