The basic idea of social overstretch is that countries can do so much to help the poorest members of society that they end up hurting the society as a whole by financially draining the economy. I do not think that we are at that point in the United States.
The real problems with the government deficit do not come about because of welfare programs for the poor like Medicaid and Food Stamps. Instead, they come about because of broader based things like Medicare and because of our general desire to have more government benefits for us all (particularly the middle and upper classes) without having to pay taxes.
We are overstretched because we in the middle and upper classes want too much from the government and don't want to pay for it, not because we spend too much on the poor.