As many as you genuinely want and can support and love. I have two, which is probably enough for me. Since I love my kids and enjoy pregnancy and giving birth (yes, really!) I would like more but I have to balance that with our finances and the time we have to spend on them etc.
Re. overpopulation, I like to think my kids will help become part of the solution rather than just part of the problem. They're smart kids and with the right opportunities maybe one day they'll change the world for the better. More than that, I think if we give up on having kids that is in effect giving up hope for the human race altogether and I'm not ready to do that.
I have friends with large families who cop people being judgemental about them having "too many kids" and others with just one who get judgement about having an only child. You really can't win. Well, people seem to be happy if you have two, but then they can't help but say something like "you can stop now", especially if, like me, you have "one of each" (a girl and a boy). There are advantages and disadvantages to coming from a large family or a small one. Kids from larger families might find there isn't as much to go around when they are younger, and have to wear a lot of hand me downs. Only children will have to bear the pressure of trying to support their parents in their old age alone and have to deal with other people's rude comments about how "only children don't know how to share" (aren't stereotypes fun!). There's no hard and fast rule but as long as you can support them it's not anyone else's business how many kids you have.
If you can't support them you shouldn't have them. Though even if you can support them when you plan to have a family things could change down the track, you could lose your job or have unexpected medical bills or something, so even if someone needs help to support their family I try not to judge them if I don't know their circumstances.
I agree that it should depend on your ability to support the children and look after each of them. If you don't have time then you should not have children at all. Remember that child rearing is very time-consuming. When they are babies, you need to be prepared to wake up during the night to feed them or to comfort the little ones. A little older, you have to care for their education, their feelings, etc. It's a life-long commitment.
I am an only child, and very glad of it. I never felt lonely as a child; I always felt much happier by myself or with adults than I did with other children. I did have a few friends up to the age of 11, but as soon as I moved to secondary school I had no interest in having friends because I found that I had absolutely nothing in common with other kids.
I don't hate all children; it is a generalisation, but I still do not want to me aroumd them. I find most are noisy and annoying, and if you are a parent you have to look after them, be patient with them, spend money on them. They become priority over yourself for the rest of your life.
I quite like seeing my baby 2nd cousin on occassion, but I can only deal with him for short periods and only when he is quiet or doesn't need feeding, changing, etc.
The problem is that many of the poorer nations are having many children whereby they can not feed or look after them. This places a huge burden on the rest of the world, with charities trying to do their bit to help. I believe the amount of children you have should be the amount you can afford to have. To ensure they have a safe and successful trip through life, they would need the necessary basics to give them every chance possible. These basics include university which can be expensive.
The problem there is that actually having a choice how many children you have is a luxury only available to those of us with access to birth control. Many people in developing countries can't afford it and they are in any case discouraged from using it by religious groups who spread lies about condoms causing aids etc.
And that would mean people in third world countries, or anyone living below the poverty line weren't allowed to have children - that hardly seems fair. You can't take away someone's right to choose to have a family just because they were born into unfortunate circumstances.
I think if your below the poverty line...and can not even feed one's self..... it's not really a matter of being 'unfair' that one should not have children.
It's unfair to have them, and unable to feed them,( I take Jennifer's point.)
I am in two world about this. I am with Bryony - that I don't want kids right now. There are too many of us as it is for starters. On the other hand, the family has the right to choose how many kids they want - provided they can be supported financially. The question: when is too many, too many?
One, or two max. The world is grossly overpopulated and it will be the literal death of us (and the planet!). And by needing to have more crops etc. to feed everyone we are also killing off SO many animal species.