Please provide your evidence there is no causal association between marriage and fertility rates.

>I don’t want to encourage more children from people whose primary blocker was child support payments

A prime reason why I didn't have kids in my 20s was because I could afford the kids in marriage, but couldn't afford to spend 20% (more like 30% post tax) on child support, as I had calculated it out. And knowing divorce is always possible, not willing to risk that. The actual cost of my kid is like 10% of my income, but because I'm married I'm not forced to spend closer to 30% as a transfer payment with no check it actually goes to the child. Without poorly thought out child support laws I'd have had kids sooner, and possibly more, and the kids would likely have been better off because when I was younger I had more energy and better genetic material to produce them.

I would even assert the people thinking ahead of time about child support actually calculated in a way that achieves roughly enough to take kids out of poverty, rather than basically a % of income, are exactly the type of people that should be parents. Under the current system child support can be next to nil, or extremely high if you're high income, rather than revolving around ensuring it is actually a number and check and balance to ensure the payment and spending is to bring kids out of poverty. The current system has less child support for poverty-born children but higher for wealthy-born children, meaning the incentives are precisely backwards from incentivizing children born into higher income marriages and the CS incentives higher for higher-income families to divorce and fall back into the lower-fertility unmarried bucket.