Complete is a strong word that I should have qualified. Mastery is a better word. Control over it. Where your emotions bend to the will of your rational mind, not vice versa.

Don't limit yourself without reason. As humans we are agents of change in an incredibly complex, chaotic system (society). Mastering emotional control allows us to become much more effective agents. Someone half as smart but with twice the self control in every area can easily beat the more intelligent opponent. Not every time, but it is a massive advantage. http://scienceblogs.com/cognitivedaily/2005/12/14/high-iq-not-as-good-for-you-as/

I didn't say that it's predictable, or that it is super easy, but it's not particularly difficult and only takes a few months of commitment of a few hours a week, to bring a lifetime of reward.

I'm surprised that as a "rationalist" you suggest mastery of the emotions may not be desirable. Awareness of one's emotions, sure. But letting them dictate your actions in any way, why? Be rational.

And one without mastery of their emotional state (that is, the experiential drag of depression, or impulsive actions of rage, or hurtful actions of uncontrolled lust, etc), one is at a disadvantage in almost any situation,