I notice you appear to agree with the pollie's statement given the heading of the thread. This includes that overpopulation causes global warming. I thought you did not believe in man made global warming?
I agree that population growth is a serious issue. Lower population means less pollution, less global warming, less pressure on resources.
Sure Japan faces problems from an aging population. That is part of the transition to a lower population. But that is being solved - more Japanese are dying than are being born as I write this.
How do we encourage lower birth rates? Education, free contraceptives are good ideas. Lower financial incentives to have babies makes sense - baby bonus, family tax benefit etc
Take away charitable status for organisations with archaic attitudes to family planning such as the Catholic Church.