Actually I have had conversations about that before. I think it's a necessary deterrent.
It's not. Read my first post (third post in this thread.) It explains why it's not a necessary deterrent.
The needs of the many outweigh the needs of the few.
This is a very socialistic point of view and even though it seems to make sense, nature doesn't work like this.
People will always think of them selves first and then about others. In other words, from the individual's point of view, the needs of the few (the person him/her self) always outweigh the needs of the many. Though people may talk like they don't believe that, if you really analise their behavior, you'll see that they actually apply the logic that their own needs outweigh the needs of the rest.
This is actually the way things work in nature. It's the "survival of the fittest" logic or "natural selection".
So when you want to solve these kinds of problems, you need to take this into account and come up with solutions that use the correct principle. This basically means that if you want people to have less babies, then you need to give them a reason for not having many babies. And that's actually easier than it seems.
Education doesn't work (though helps) because it doesn't change the individual needs. Educated people say that the needs of the many outweigh the needs of the few, but if you have no reason for having just 1 or 2 babies instead of 6, then you will have 6 babies.
What changes people's needs is economic stability. Once a population has economic stability for a long time (multiple generations long) then you see the need for having lots of babies go down a lot. Because in that situation, the believe develops you can give your children the same as or even better than, you have. In that situation, the need for having just a couple of babies is bigger than the need for having lots of babies.