We all know how crowded London is. It can, at times, be a very unpleasant place to live. So it's a little disturbing to see that Britain might have a population of over 75 million people within a few decades.
For all the positive things people can do towards saving the planet, only having one child is probably the best one. We are at a stage in our evolution, physically and mentally, whereby we can reduce our population significantly and not suffer too much economically and probably see increased social benefits from smaller communities.
Less people means less waste. Less people means more space. Less people means an easing of the housing crisis.
Win win in my opinion.