Eliminating any one emotion would have an adverse effect.
Take 'regret' for example. If you could not regret something you've done, accidentally or purposefully, what is there to make you learn from the error or mistake?
Without 'sadness' you would not have 'happiness', you'd just have a constant state of 'meh'ness. (go with it, it's 1.30am and I can't think of the correct word.) Likes and dislikes would be affected, and what about hobbies? Would they exist?
You need the two opposing emotions, both negative and positive, to have any range and to get the full feel for life.