I'm nearly 40, the internet that I grew up with, is vastly different to the internet my kids are growing up with. Heck, the internet the 15 year old grew up with is vastly different to his 4 year old sister's experience.

I see nothing wrong with blocking access to certain sites by default - protects us as well - if anyone of them have a problem with it, they can come and ask why it is blocked. Simples.