A few days ago, I stumbled across this, and though pretty much everything I wanted to say had already been said in some of the comments below, I still felt compelled to jot down some of my thoughts on the issue.
Obviously, I disagree theologically with the author. He's Christian, I'm Jewish. However, I have heard the same argument repeated in various forms and guises:
"You cannot shelter them from the world" - not when they grow up, certainly; but as long as your children are young, it is actually the parents' duty to shelter them as much as reasonably possible from what they see as a negative influence. Previously we have had the misfortune to be often in company with a man who absolutely could not and would not watch his mouth. Every time we encountered him, I had some very awkward questions from the girls ("what is a homosexual?"). Eventually I began taking an effort to avoid this man. That's because the girls were 5 and 3 years old. I felt absolutely no scruples about avoiding such confronations. Had they been teenagers, my attitude of course might have been very different.
Almost all parents I know use discernment when deciding what sort of movies their children can watch, what internet content to allow, whether the children can have a Facebook account and at what age. What is it if not sheltering? Thus, if parents feel that the local public school can and will damage their children, and think that the best educational option would be to pull their children out and teach them at home, I see it as absolutely justified.
"It's immoral not to be part of society. Everyone should be schooled together" - This goes beyond the homeschooling argument. This actually implies that only one type of schools should exist, with uniform program and content. In Israel, there are secular public schools; religious schools on a wide spectrum of Orthodoxy; alternative schools; Muslim schools; Christian schools. People can and do separate into groups according to their religious and moral values, and want their children to be educated according to said values. It is natural and it has always been so, and always will be so, and trying to artificially weed this out results in tremendous injustice and trampling of human rights. At the dawn of Israel as an independent democratic state, Jewish children from North African and Yemenite religious families were forcibly or near forcibly sent into secular education by the more "enlightened" European-descended founders. This is not democracy and is still remembered with indignation by many people.
"Your children can be a good influence in a bad environment" - In Israel, there's a long-standing public conflict, at the heart of which is the refusal of Charedi (so to speak, "Ultra-Orthodox") Jews to serve in the IDF. One of the arguments of the army avoiders is that the army does not provide a culturally acceptable atmosphere for the young Charedi man, even one who isn't capable of becoming a full-time Torah scholar. This can cause much bitterness while a large slice of the population is risking their lives for their country, and others are shirking their duty because of seemingly petty excuses. However, there is no denying that a secular environment promotes secularism in isolated religious individuals, far oftener than such individuals can reform a secular environment. When my husband went into the army, he remembers being quite shocked at the mixed male and female environment and the lack of modesty it promoted. He told me that nearly all his Orthodox friends who joined the army experienced a slipping of their religious standards. It was simply a lot more difficult to keep up in an environment which was not supportive.
The question of women in the army is another one, and too charged to be lightly discussed here. I only meant to use this as an illustration. These are adults, with adult struggles. What, then, can be said of children? What are the chances that children reform a government-funded system run by adults whose authority they must obey? Think basic nature laws. Drop an ice cube into a bucket of boiling water. What will happen? Will the single ice cube be able to cool the whole bucket? Or will it melt instantly until no difference is felt in the temperature of the water?
It is no wonder, then, that though few people in Israel actually homeschool, most - and especially Orthodox Jews - take an effort to find a school which will represent their values as closely as possible.