This is the big one. If we all want to live the big life - cars, flights, meat, AC...then we have to procreate less. Otherwise, we will literally breed ourselves to extinction, and as agent Smith put so well in the Matrix, we'd be no different then viruses:

Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment; but you humans do not. Instead you multiply, and multiply, until every resource is consumed. The only way for you to survive is to spread to another area. There is another organism on this planet that follows the same pattern... a virus.

Instead of encouraging procreation in our tax laws, have parents pay a carbon tax to offset their offspring's pollution.