You are right about the Guardian's agenda, Dickens. I read it, and have done so for decades, but question the bias just as I do when I read other sources. I also read the Telegraph, and coming from my political persuasion I do find it comes from a very obviously Tory (and a particular type of middle class/older/white/traditional type of Tory) perspective. That's fine - I have no problem with people having different views - I just allow for that when coming to my own conclusions.
I only see the Sun or the Mail when there are links from somewhere like here, and I apply the same judgement, bearing in mind the types of publication they are. IMO the sort of 'you must be gullible to even read that' attitude is every bit as narrow-minded and lacking in nuance as the papers themselves. People can use judgement.
Also, there is nothing wrong with taking even the most outrageously biased (or even bigoted) headline as a starting point for a discussion. If a paper ran a story about banning the sale of milk to be kind to cows (^they haven't, and AFAIK there is absolutely no move towards making this happen^) there could still be a good discussion about animal cruelty, farming methods, veganism, the rights and wrongs of 'banning' things, and so on.
I think this is true of most threads on a range of subjects, but on this one we are discussing the level at which sex education should be taught to younger children. The spin put on the story by various papers isn't particularly relevant to the debate. This is a discussion site, not a press agency.