It's uncouth to use the word in this context, but the intended analogy is simply that of theft or plunder, which is a well-accepted definition of the word and is in common usage.
The original definition of the word "rape" refers to a theft or seizure of some sort, so the usage here is accurate, given the focus is on the metaphor of the wallet and not the person directly.
Child support laws frequently have little to do with supporting children. Payments are frequently far higher than necessary and far higher than the non-custodial parent can afford. There is no accountability at all on the custodial parent's spending, while the non-custodial parent gets their wage's garnished so they can't even pay their rent.