My position is quite against the flow on this, which surprises me because I am firmly against most attempts to control my access to information, or decision making.
Anyone who caught a glimpse of Joseph From Essex on ITV's recent jungle programme will probably share my amazement that this fully grown man did not know how to tell the time. He explained that he'd had an iPhone since about 7 and, well, "it's on the front". Each generations capability with the internet greatly surpasses the previous. It is clear to all, I hope, that it is nearly impossible to avoid pornography online, and it would be irresponsible to not try and protect the development of younger children.
We can't choose our parents, and whilst most would install their own filters when introducing technology to their kids, there are those who just couldn't give a toss. Or more likely, they're still trying to figure out where to put the installation CD.
I do not see the problem with an ISP having a default filter, with quite a broad scope, on the strict conditions that (a) the fact my search is filtered is very clear; and (b) I am able to easily switch it off.