That's because women don't decide to have children in order to get welfare, they decide to get welfare because they got pregnant. Also, as a community starts to go downhill, couples often have less access to birth control and other family planning options, especially those who are "just getting by" to begin with.

The only people who actually seem to think that welfare causes these problems, are the ones who don't think we should be paying welfare. People who are on welfare or know those on that kind of assistance know better.