Most states base child support on an income shares model, basically the more you make the more you pay. Yet there is only one parent who is allowed not to work, and that is the custodial parent. Regardless what federal law states (which btw, is that BOTH parents are financially responsible for the child) state allow custodial parents to either stop working or not work at all.
This really becomes a problem during a second marriage. As an example, take a couple who divorces and the custodial parent works after the divorce. The non-custodial parents CS is based on both of their incomes. Now if the custodial parent decides to have another child and quit their job, not only is can the amount of CS be raised on the non-custodial parent that same parent can actually have their CS raised on the notion that the custodial parent now has more of a financial burden due to the new child.
I hope you followed that line of reasoning the states use, since I've yet to see how the states can impose CS based on a child the non-custodial parent has nothing to do with.
Read Roger's post previous to mine & follow his link or you're not talking about the same thing I am. It looked to me as though the proposed VA statute addressed your complaint, where the cost of living in the non-custodial parent's home was taken off of the top.
As far as parents "allowed" not to work... I know of several interstate cases that would make your position bunk. Meaning, as they are interstate cases, federal law applies In those cases, as long as the ordered obligation is paid, the non-custodial parent's working or not working isn't addressed by the court.
I know of cases in income share states where the custodial parent's income is imputed.
Finally, it looked to me as though *both* households are lible for a hit if the other household chose to have additional children (reduction if in NCP household or increase if CP household). If you re-read my post, you'll see I took that into consideration, which is why I said, it would be a second hit for un or under employment. Where is Agnes with her pie theory when I need her? lol