My family is fortunate because my husband is brilliant in math and science. He teaches my son in the evenings. He and my son enjoy this interaction. My son scored a near perfect on his SAT's regarding those subjects. (My son just turned 14.) We know homeschooling parents that aren't as proficient in math and/or science, but their kids do just fine by utilizing used textbooks, the internet, software programs, science museum seminars or hiring a tutor. (My husband tutors one of my son's friends in math.)
My husband was never that keen on biology so he has our son attend a Santa Rosa Junior College course. My son will probably take a chemistry course next year even though he and his Dad have set up a pretty good lab in the garage.
Of course, not all homeschooling families can afford tutors, expensive software or internet courses, but somehow they manage. If their child is motivated and talented in certain subjects, all sorts of options (and blessings in regards to funding) open up! I've seen this happen time and time again.
Let me state up front that I think alternative schooling is a great thing.
However, I just like to call things what they are. EVERY time someone sends a kid to a college course, a public school athletic team, and co-op of kids taught by one knowledgeable parent, etc., they are simply recognizing why institutional schools developed in the first place.
What homeschoolers and private/parochial schoolers want is legitimate input into the content and methods of THEIR children's education. I fully support that...especially in terms of moral education.
But we shouldn't pretend that the bugaboo is the "institutional" school. The devil in the details is threefold: (1) Schools off on their own "immoral" education crusade, and (2) Schools that have lost control of discipline, and (3) Schools with low academic expertise.