We're talking about development, urbanized countries. In those, you having children leads to economic growth and other positive effects in the long run.
There are a lot of places where you agree without actually agreeing. See taxes, citisenship and EULAs.
Even in urbanized countries, I think there is a sweet spot for the number of children that should be desirable vs what would cost you massive problems later on. If you are talking about having 2 children just to renew the generations, I have no problem to follow you on that path, but more is questionnable when you already have massive unemployment, a crumbling debt on the whole of society and an education system which has become the synonym for disaster. Growth comes from solid standards, not from loose ones.
About your second comment: maybe it's just about words, but technically speaking you do not "agree" with your citizenship, you are just born with it. It's like having parents, you do not "agree with it", it's just given. And this is different from EULAs where you do "agree" (since you have to signify your agreement explicitely) while the legality of the EULAs is, in general, highly questionable.
There are a lot of places where you agree without actually agreeing. See taxes, citisenship and EULAs.