Is population growth the cause of our troubles?A green myth is on the march. It wants to blame the world's overbreeding poor people for the planet's peril. It stinks. And on World Population Day, I encourage fellow environmentalists not to be seduced. Some greens think all efforts to save the world are doomed unless we "do something" about continuing population growth. But this is nonsense. Worse, it is dangerous nonsense.  For a start, the population bomb that I remember being scared by 40 years ago as a schoolkid is being defused fast. Back then, most women round the world had …