I am 40 years old now, so this was quite sometime ago, but my parents were divorced when I was six. My dad would voluntarily raise the amount he sent to my mom every few years.... In addition to paying for extras like school trips and sports lessons. So not ALL are jerks.
Yep, I'm going to stick up for the non custodial parents here. Sometimes they deserve to complain. Sometimes they deserve to complain but don't because they are just stand up kind of guys and the women they married are deadbeat parents.
My brother pays a huge amount in child support, which he does because we have the income based (both parents are assigned a percentage of care with the parent who makes more paying the difference to the other parent) support. He has never complained about supporting his kids.
However his ex wants the most expensive private school in our state, which they are supposed to split 50/50. My brother pays for 75% instead because she cant "afford" her half but she is threatening to take him to court because he won't pay her portion, for the school of HER choice anymore, even thought the boys are not doing well in that school and want to transfer. He pays for all the sports fees and equiptment. He buys most of clothes/shoes/needed items. Half the time we find out they need a particular piece of clothing for something immediately, but their mom hasn't bothered to go buy it. He pays for the majority of their incidental expenses. She is stalling on my nephews braces because she doesn't want to pay for her half of the deductible (my brother pays for the entire insurance premium).
They have shared custody but she is custodial (though now that the boys are 14 that's about to change as one of them is already planning to move in with his father this summer). My brother takes them more than his allotted time because she needs more time to do things with her older son (not my brothers, but she did actually try to get him support and insurance in their divorce).
She works for a family business, she buys everything on the company card which she doesn't have to pay for. She gets more in support than many family's monthly paycheck, and even though the economy has lowered his income he has never taken her back to court to lower his payments.
She's bad with money, she wants my brother to pay for everything and support her and her oldest son, and bad mouths him to the twins. She sucks, but some men do put child support first, and the welfare of their children above what's fair to themselves.
So I never automatically side with the custodial parent. They are just as bad as the non custodial ones just as often.