Avoiding Cognitive dissonance,is it a necessity?
I think you're confusing science with politics.  The APA and other such professional organizations have not, to my knowledge, concluded that cognitive dissonance should be avoided or even minimized.  I'm unaware of any evidence that suggests that cognitive dissonance directly causes distress or suffering.

The position of psychology, as a science, is that cognitive dissonance is a phenomenon that exists and has certain properties.  There is no normative stance from the field as a whole.

What happens in these cases is that political groups engage in activism and argue that such things should be minimized; the same is true of stereotyping, for instance.  You may agree with the dominant political opinion, but it's not a scientific question, per se.