Every family has that one kindly aunt and uncle who "never had any children." And, until you yourself have struggled with infertility, you probably never wondered why they had no children; you just accepted it. Well, if that aunt and uncle of yours are now seniors, in their day they could have adopted from a wide assortment of newborns. But they didn't. Today, they probably live comfortably in a small condo somewhere, travel a great deal, are enjoying their retirement, and dote on a large selection of nieces and nephews. When they pass on, they'll probably leave their money to their "favorite" niece or nephew and will always be fondly remembered.
Now, compare that lifestyle to the "other" aunt and uncle who have three miserable sons who "eat their hearts out." Everyone in the family knows that these sons scammed their own parents out of their life savings. One son is a stingy businessman who nobody in the family likes, the other is a cocaine addict who sold his father's collector's edition car to buy more coke, while the third son is a bum and has never worked an honest day in his life!
I exaggerate these two lifestyles to point out that there is no guarantee of happiness either way. Some couples with children wish they'd never had them; couples with no children may regret it. The decision itself is not as important as how comfortable you are with your choice.
In the past, a child-free lifestyle was often a political decision for many couples. During the 1950s and 1960s, many couples chose this because they feared a nuclear holocaust. By the 1970s, the issue of overpopulation became the motivating factor for the choice. For example, research at Cornell University recently concluded that the world's population must be reduced from its estimated six billion to roughly two billion by the year 2100. However, population predictions for that year, given current fertility trends, are for roughly 15 billion. Once we factor in available natural resources, energy reserves, and arable land, a world population of that size would throw the majority of individuals living at that time into "absolute misery, poverty, disease, and starvation" (according to the Cornell paper).