No, they are not mentally imbalanced, or you need to regard your own child who waits for father Xmas so too. Many religiously reared children like me become suspicious of the doctrine when growing up, as it does not follow reason. To my mind, religion is a crutch which gives many people comfort and peace. Humans, being what we are, know that death comes to us all and can not rationalise it, therefore religion is viewed as one answer. Even Darwin turned to religion to pacify himself when death become imminent.
The ones that get up my nose are those who stick their beliefs down your throat and are hypocritically inclined when it suits. Most 'believers' live a normal life and are happy to live their lives roughly by their church's doctrine. I am somewhat envious of the ones that find solace in their religion when they lose a loved one, or can justify the the rampant cruelty that occurs daily on this planet.