The government is effectively trying to tell parents how to raise children. This will horrify some, reassure others. It's essentially similar to the Great British Smacking Debate. Interventionist, statist liberals will invariably think that the social consequences of allowing unfettered parental freedom are simply too great, and can be measured (crudely) in the number of teenage pregnancies and knife-crimes littering Daily Mail front pages.
Conservative liberals, NIMBY 'my home is my castle' types - with whom I often self-identify - will usually find this a shocking encroachment of their freedom to live as they choose, and raise their children according to their values.
I sympathise with the liberal interventionists on some things, e.g., howsoever much a militant father wants junior to be a fully-fledged toddler-commando, replete with bare-knuckle training and cot-based automatic weapons fire, I think it is legitimate to save children and society from manifestly unsuitable parenting. That's a no-brainer for most people.
Morality and taxationOn this issue, however, I'm with the instinctive knee-jerk liberal brigade. Prescriptive sex education is something you get in religious schools and communities as well as households. The government is effectively saying, 'we know you believe this stuff, but we think you'll fuck your kids up by indoctrinating them with it.' Not the classiest nor the most demonstrably consensual use of conservative tax-payers' tax pounds. It's illegal not to pay tax, and then you find your money used against you and your way of life. That must suck.
As tempting as it must be when you suddenly find yourself with the power to spend other people's money to tell them what to do, I's appreciate it if governments interpreted their role in a morally narrow, neutral and consensual manner. Government should protect us, provide our infrastructure and services, and basically nothing else.