TW, I'm not sure where to begin. Is the idea that being an adult means no longer entertaining emotions something you have come up with on your own, a school of thought taught by some one, or something that you were taught growing up? My 16 year old son gave me a hug today when I got home, this produced in me a profound feeling of happiness.
I entertained that emotion, and thought about the different levels that this made me happy, I won't go into all of this right now. I would say that emotional maturity does not mean we don't entertain emotions as much as we understand the context of emotion in our lives and the consequences of our actions along first, second, and third orders of effect. The beliefe that airborne will keep you from getting sick on an airplane is a problem with logic, not emotion.
The emotion of compassion has produced in people the desire and ability to take unselfish actions that have improved the conditions of this world and the people living in it. This has added to the happiness experienced by many people.
Here is a link that I think you may find interesting.
This only one example out of countless that I could show how emotion can be useful.