Maty - Re: false assumption?
> Can anyone point to a definitive study that shows harm being done?
No, because there isn't one. There's lots of anecdotal claims, but they're generally based on the idea that "they saw porn therefore they did XYZ" and ignoring any other influences that may have been around.
On the flip-side, however, is the work of, for example, Professor Milton Diamond PhD of the University of Hawai'i who studied the effects of the increased availability of porn in Japan and America and concluded:
" It is certainly clear from the data reviewed, and the new data and analysis presented, that a massive increase in available pornography in Japan, the United States and elsewhere has been correlated with a dramatic decrease in sexual crime"
Unfortunately that didn't stop the last government introducing their Thought Crime "Extreme Pornography" legislation, nor, I have little doubt, regrettably, will it stop David Cameron from introducing a law making possession of videos of "consenting non-consensual" porn (ie acted out scenes of "rape" by consenting adults) a criminal offence as well.
You can (for whatever good it will do) sign a petition to object to this here: http://epetitions.direct.gov.uk/petitions/58255