But children? I just don't see a situation where the child is fully capable of understanding the whole situation.
What's to understand? I keep hearing this statement made. If "understand" means "know and be able to responsibly consider the potential consequences of the act," then I think this is just as much of an argument against sex among adults.
If "understand" means "realize that sex is dirty / sinful / for adults only / for married people only / for people-in-romantic-love only," then I say that these restrictions are purely socially constructed and thus it's coherent to discuss the possible alteration of the social norms.
Personally, my bet is that antipædophilia laws are designed to protect the privilege of adults who want to control the biology of children, not to protect the children themselves. This should not be too surprising; quite a lot of common law is oriented around protecting somebody's privilege to control somebody else's body.
Wow, what a topic! How to argue about an emotionally charged topic without getting emotional.
More than half the adult women I know were subjected to adult sexuality while they were children. From their discussions on the topic, I do not believe it is true to say that the child is unharmed by the practice.
The biggest harm comes from the adult manipulating the child into preforming the acts. The abuse of power, whether by physical, emotional, or "economic" advantage, leads to an expectation that adults can not be trusted and that the child's value is not relevant.
For example, a certain child's grand parent threatens that if the girl does not perform for him, he will just use the younger sister the same way, and if he is "tattled on" he will be arrested and they will lose the house they all live in.
An adult has many advantages over any child, and when they use these to force a child to do something deemed legally and morally wrong by society, it is damaging to the child's development.
Consider this, in arguments for pedophilia, substitute bestiality. the two are much the same. The subject is not in control of the situation. The subject has less rights, and often has no one to protect what rights they have. The difference is that we tend to be less concerned about the development of the beast, and the best is less likely to perform the same acts when it grows older. And since a large number of pedophiles attack family members, there's the whole incest thing too.
Depending on the age of the subject, the acts can be physically damaging, psychologically scaring, they are acts of abuse.
Sure there are gray areas. Do you prosecute the 18 year old boy friend of a 17 year old girl (or 18 Girlfriend of the 17 year old boy)? What is the most rational age of consent? What if the youth is lying about their age?
They are why there are courts and judges. The law is established to set standards, the system is supposed to apply them in a rational manner.
I have an 8 year old boy and a 12 year old daughter, only in a twisted mind would anyone consider them as a fit object for sex.