With definitions, language, and the difference between fantasy and reality.
For example:
I made clear my views on the following:-
a) Sex with children: Bad - don't do it.
Why? Not only because it is impossible to be sure the child is doing it completely of his/her own free will, rather than feeling under some obligation, but because the risk of harm - both physical, from the act itself - and emotional/psychological, from the emotions involved at the time and the reactions of others - is too high. And any non-zero risk is too high. (And if you do, you can get put away.)
b) Child Porn: Bad - don't do it.
Why? Because, leaving aside the proportion that is obviously film of child abuse, even if the kids look as though they are enjoying it, how do we know what conditions it's made under? They might like the activity itself, but are they really doing it just because they want to? Or are they doing it because it's the only way they can get food and shelter, or because they are scared of what might happen if they say no? If you enjoy looking at pictures of people who are in situations they cannot control, doing things they have no choice about, what does that say about you? (And if you do, you can get put away.)
c) Taking photos of kids in public places: Bad - don't do it.
Why? Because at the very least, taking someone's picture without asking them is rude. And if you intend to take them to drool over, that reduces a complete stranger, who you have already considered unworthy of even asking permission, to the level of a sex object. This shows a lack of respect. Do you disrespect children that much?
d) Taking photos of kids and posting them to the internet: Bad - don't do it.
Why? Because this is the same as above, but multiplied manyfold. It's bad enough that you think someone worthy only of being used as your own room decoration, but when this picture - remember, taken without permission or maybe even knowledge - is posted in public, for other people to drool over, this doesn't show a lack of respect, it shows a complete absence of it, along with a total disregard for the person's feelings.
In another blog, some people, when given my opinions above, complained I "hadn't got it", "didn't understand" and such, along with abuse and a fair smattering of four-letter words (always a sign they can't think of anything else to say), and went so far as to have my blog removed. The curious thing is, it wasn't a pro-child-sex "I do what I want because they like it really" militant paedophile blog, where one might expect such a reaction, it was an anti-child-abuse kid-sex-is-wrong blog.
I respectfully propose that it's they who haven't "got it", and certainly don't seem to understand that when I say "don't have sex with kids", I actually do mean "don't have sex with kids". Children are much too beautiful and valuable to risk harming them.