Why is it taboo not to love your time in the service?

I am perplexed by the idea that everyone who put on the uniform has to love what they are doing. How is it that you expect everyone to be able to have the few goods override the many negatives? We all know that every day we lose great talent because they are unhappy with the work conditions, and no longer want to tolerate them. We speak about how we might be able to retain them if possible. I understand not everyone can retire from the military but like any other company shouldn't the Army be doing its best to retain as much prime talent as possible?

I learned a lesson as a child in school, "you do not have to love the job you have, but you have to do it to the best of your ability". In the military I learned, "if you don't like the way things are, get promoted and change what you can in your A.O., or get out and lobby for change from the outside".

Maybe this is a rant, but I have some real interest in knowing why it is so taboo for people when they hear you are not happy about your service as of yet, or your overall experience in general.