That's a good thing as long as we don't reach European levels in which the boomers/old age are now tipping higher than working class or somewhat an inverted population age which could be bad for the economy
Depends on your perspective. From a global perspective, probably a good thing for environmental reasons, based on a resources-per-person metric (you know, like disposable diapers). It's mixed if you're thinking as China, (or anyone else we owe money to) since their ascendancy is in a large part built on American dollars. From an American point of view it's mixed as well. A declining birthrate may lead to more wealth being concentrated in fewer hands in the middle class, and it will certainly shrink the labor pool so that American workers (some of the most productive in the world) are able to command higher wages. It's terrible news for the health care industry, since there's already a shortage of qualified employees to take care of our elderly. It's probably okay for agriculture since we're one of the few places that has both the technology and space for intensive, large scale, automated agriculture, and we'll always be able to sell our wheat and soybeans to the rest of the globe. Especially considering that countries like India and Africa are growing rapidly and food insecurity is rampant. It's not really good or bad; it's just a thing that's happening.