From: Another Engineer [Email him]
As a fellow engineer, I feel compelled to add to my colleague's analysis, which showed that low birth rates do not necessarily lead to decline of a people since dependency ratio increases in older people are compensated by decreases in younger people. Unfortunately, in the presence of immigration, a people who are reproducing at sub-replacement levels are simply replaced by the immigrants. This is what Western peoples are facing.
Most tragically, the increase in population leads to increased land and housing costs, competition, and increased costs for services such as water and public infrastructure growth.
All of these costs must translate to lower fertility for the natives-born. They can afford fewer children; women must spend longer in the workforce to pay for a larger mortgage; they must delay starting a family while they save for a house.
I am conscious of the tendency that the same people who are part of the Open Borders Lobby are also fans of birth control at home and often vocally "anti-natalist" in terms of providing any real support for native-stock Western birth rates—for instance, widespread availability of childcare within walking distance of workplaces; and ways women can leave and re-enter the workforce with greater ease.
A mother re-entering the workforce could be treated as if she were a minority and favored. But such pro-natal programs allegedly degrade women into "baby making machines" and are "Nazi Like". This attitude betrays a desire for demographic replacement. Yet the sheer cost of modern housing and education, caused in no small part by immigration and the fiscal support of the burgeoning protected minority population, means that some kind of support is essential to allow couples to start families while they are still biologically able to do so.