Did you intend to talk exclusively about virtual child porn? If so, you might want to change the wording of your initial assertion, since "virtual child porn" is not what people think when they read "child porn".

If not, I don't think you've adequately supported your assertion. It may be the case that viewing child porn does not increase the probability of committing child abuse once you've conditionalized on relevant common causes. But it is the case that producing child porn (actual, not virtual) requires child sex abuse. Since increased availability would presumably be causally linked to increased production, ceteris paribus increased availability should be causally linked with increased abuse. Now it may be the case that there is some countervailing causal mechanism leading from increased availability to decreased abuse, but you haven't really provided adequate evidence for the existence of this mechanism, or that it fully compensates for the increased abuse associated with production even if it does exist.

Also, when you say that child porn with real children should be illegal, do you mean that just production should be illegal or that possession should be illegal as well?

And this:

In any case, one of the rationality principles does say that arguments should be evaluated on their own merits, not the attributes of the person making them.

This is not right. The attributes of the person making an argument are often valuable evidence regarding the validity of the argument, especially in an area where one is not an expert. For instance, I don't know much about the research about the relationship between child porn and child abuse. You haven't presented a comprehensive meta-analysis of this research, merely a selection. If I'm trying to evaluate whether your framing is representative of the actual state of the research or whether it is cherry-picked to favor a particular position, my beliefs about your personal attributes are very relevant.

As an aside: I'm really not comfortable with a single-issue poster whose single issue is pedophile rights, especially if this slides from advocacy for celibate pedophiles (which I don't consider objectionable) to advocacy for consumers of child porn (which I do consider objectionable). Consider participating in other discussions on this site as well, so that people don't get the impression that you're on here just to push this, shall we say "provocative" agenda. I feel somewhat bad about saying this because I dislike the idea of piling on to posters who voluntarily identify themselves as low status, and also I do think your commitment to celibacy and the avoidance of child porn in the face of your unfortunate desires is commendable (although I don't like your attachment to pedophilia as an identity). Still, I haven't downvoted you yet, but if every top-level comment or post you make ends up being about pedophilia, I might start doing so.