The images of violent porn, defined as "material featuring violence that is, or appears to be, life-threatening or is likely to result in serious and disabling injury" isn't my thing, but the law is focused on one case in which the killer-- who killed his victim by strangling her with a pair of tights and kept her body in the freezer-- looked at internet sites that were connected with the "fetish".
1.) The guy is insane. Whether he surfed websites or not doesn't cause him to kill.
2.) This makes the connection that his obsession with his fetish caused (or was at least instrumental in aggrivating) his killing actions. I say that correlation is not causation, but this isn't even correlation: consider that the website has likely thousands of viewers; how many of them are killers. This freak of nature is an anomaly in any consideration, and making "violent porn" illegal to own because of this is dangerous to freedom issues.
3.) The definition is ill-defined enough that it could start infringing on more mainstream fetish porn, particularly bondage, which is mainstream enough to affect millions of people.
It's a politicized morality ploy.