2) Each unhappy population slows down your growth rate without giving you anything in return, and possibly forces you to work more food tiles without getting anything from them. Also, the unhappy population doesn't give anything, but adds unhealthiness.
How can you say unhappy population slows down growth? Unhappy population is basically growth that has already happened, how could any growth be faster than that?
Unhappy population gives nothing, true, but it doesn't cost anything* either. Unhealthiness is just food, and you already had enough food to grow once.
It would be nice if there was a governor option "Work to eat." that made the governor only consider working citizens when deciding how much food to produce, but most of the time it works well enough.
Come to think of it, that sound like a fairly simple mod that wouldn't have any negative effects. Just find the part in the AI where the food needed is calculated and replace current pop with happy pop.
* Apart from the events that can happen with unhappy pop. Those are necessary to make unhappy pop have any cost.