As someone who has paid monthly child support for the past 8+ years, I often wonder how many exes who receive monthly allotments for the care of their children actually spend that money on their child and/or put it away for the child's future needs.
Spousal support is meant to assist the lower-earning spouse who, usually, has spent more time during the marriage taking care of the children than developing a career. The idea is that temporary payments from the higher-earner will help get the other spouse on his or her feet and become financially stable. In California spousal support is granted when such a need is demonstrated, but for a finite period (usually just a few years following separation).
Child support, on the other hand, is granted according a formula concocted by the state for the benefit of the child and is in effect as long as the child remains in the care of the parent receiving the support (regardless of whether that parent is a sole or joint custodian). Child support is intended for the child, but because an ex-spouse either didn't qualify for spousal support or it ran out, child support payments often become de facto spousal support (tax-free, I might add).
This can and does happen because, while we have a robust system to deal with "deadbeats" who don't make their child support payments, there is no system to verify that the child support payments being received by the qualifying parent are, in fact, being spent on or put away for the child. Why is that? If a child earns money as a minor, from television or modeling work for instance, some states have laws and regulations that protect that child's earnings from being completely squandered by a parent or guardian. California's Coogan Law is a famous example of such protection.
I understand that in most cases both parents are doing their best to make ends meet and provide for the future, but it also seems to me that if a parent is receiving money to benefit the child and spending little or none of that money on the child, it's no different than using the child's earned income for themselves.
I imagine many parents using child support to supplement their own income might argue that they need or deserve to use that money however they please, and while the legislature saw fit to make a distinction between spousal support and child support, they provided no recourse to enforce that distinction except the conscience of the receiving parent. One hopes that the best interest of the child is all the conscience needed, but unfortunately this isn't always the case.