Sure it is, and it always has. Populations grow and die. That's true for the world population that both grows and declines, and for individual countries such as France that can barely maintain itself. We all agree that tax-cuts are not give-away's, they are reduced confiscations.
Should the state encourage population growth? We're talking value systems here -- what is important to us. Two things that I say are valuable are justice and the continued existence of the American Republic. People that raise children make it possible for the country to exist in the future. Since it is physically impossible to make those who benefit (the future population) pay back to those who sacrifice (forbearing population), most people consider it fair to require current grown children to pay back current parents (school taxes, child support tax breaks, etc.). Over time, not all countries of the world have gone along with this, but most countries that survive today did.
There are lot of people alive today don't give a damn about what happens to the world after they're dead. Screw 'em. Let's try and leave this planet in the same or better condition as how we found it.