Critical words bolded.
I don't "believe" in statistics. I assess their validity.
Porn is more legal now than it has been in the history of the Republic. The legality of porn has increased since the 1970s.
Therefore, the incidence of rape should likewise increase.
Unfortunately for the thesis, the incidence of rape has declined.
Therefore, the statistics used to support the argument are not validated, and thus do not support the argument.
A case could plausibly be made, then, that the increase in the availability of porn has reduced the incidence of rape. Perhaps by providing a harmless outlet, or perhaps by keeping those inclined to act that way indoors watching DVDs or downloading it off the internet rather than on the streets looking for victims.
Not necessarily. Where rape is concerned, statistics are a little squirrely. One would have to assume all incidents of rape are reported, and we know they are not.
It could be argued that fewer instances are being reported because the definition of what is rape is less clear to young women. (By that I mean, 'date rape' may be occurring much more frequently, but it's not reported because the victim's don't think it fits the criteria for a rape.)