The welfare state puts the pinch on reproduction by the productive and is an incentive to the non-productive to reproduce.
How exactly is that true?
Lots of good points made in support of my contention, but I'll add a bit to them.
Children cost money to raise. In the old days, there was an economic advantage to big families. There is no longer an advantage to having a bunch of kids to help run the farm, since so few of us live on a farm, anymore.
So, to the productive, children are a luxury on which to spend disposable income. The more disposable income, the more children one can afford.
In addition to money, kids require space. Do some demographic googling. You'll find that the places in America with the most costly real estate & rents are the places with the fewest births per woman of child-bearing age.
Things like taxes, regulations, zoning, etc. all drive up costs or reduce net income.
These days, most households require both parents to work to stay "middle class" and pay the taxes that have grown over the decades When Mommie is off at work, she can;t take care of the kids. Paying someone else to costs money, too, so each family must find the right balance and hopefully optimize their situation.
Of course, it isn;t all economic and there are other contributors, but economics is a big one.