No, we should abolish Social Security and have children according to our desires for familial idylls...or whatever. But, from a strictly logical point of view, if a community declines into a negative birth rate, it eventually disappears, whether the elders depend on Social Security or not.
But, SS isn't going away, and the elderly will want their just dues that they paid into SS...and it won't be there if the don't have children AND are opposed to open borders. THAT's the not-immediately-clear point I was trying to make.