Can you elaborate where you are seeing this? Is this as the post-secondary level or lower? I worked in higher-ed in the US and almost uniformly our institution and those we talked to in mailing lists were adamantly anti-blocking. Remembering back to when I was in HS and our library was outfitted with a few donated computers that shared a 56k connection, I know they had a net-nanny installed, but that was quite some time ago.