>humans basically evolved to handle childcare as a society

On that, you are right. It's incredibly frustrating for many trying to raise a family in Western-style living arrangements being so separate from their extended families and community. Child-raising is most efficient when done by a group: alone, it's exhausting and challenging and it's bad for the economy in the long term:

http://www.historyfuturenow.com/wp/why-the-nuclear-family-ne...

Even if you don't care about the emotional aspect, there are many impacts on society caused by the very recent rise of the Nuclear Family.

Don't forget that even childless adults are sometimes put in situations where they need time off to take care of someone else, such as a sick spouse, sibling, or parent. Having a system where theses events are accepted helps companies retain their employees through times of crisis.