My sense is that we do see defense at approximately the same rate as attacks (if not higher), but the attacks stand out more because negative emotions weigh more than positive ones. Even if we didn't see equal rates, that would be expected for the same reason: someone who hates that their parents homeschooled them is far more likely to get on and post a scathing comment than someone who loved the experience.

Companies have to bribe and cajole customers to leave positive reviews because otherwise the few people with disastrous experiences will be the only ones who bother to review at all. There's no equivalent pro-homeschool lobby begging people to get on and defend homeschooling on Hacker News.