You certainly make a valid point, but I don't think you need to worry. Although more and more secular parents are indeed starting to homeschool, the demographics are clearly with the religions families. In my experience, most of these secular homeschooling families have only one or two children while the religious homeschoolers I have met tend to average around six. Since homeschooling children tend to become homeschooling parents at a much greater rate than the general population, I doubt that the numbers of secular homeschoolers will ever become significant.
And thank you for adding me to your ping list.