There are many sad, potentially relatable aspects to this situation, the experiences he must have had to shape such objectifying and toxic views, the sense of failure he must have experienced as a result of his failure to conform to what he perceived societal views of success were, pressure he may have faced due to his economic status, and (now that it has emerged) the failure of psychiatric services to adequately resolve his issues. It is possible to acknowledge many tragic elements within the event, while simultaneously acknowledging how deplorable the event (and indeed, aspects related to it, such as his misogynistic, cruel views of others) was. By somewhat dehumanising him, viewing him solely as evil or depraved, it seems almost fatalistic, as if the event could never have been stopped and nothing could have been done to prevent it. While that view is one that somebody could have, you're left wondering what you actually do with such deranged people in this instance? Do you simply lock them away? Do you feed into the feeling of persecution? There's not really an easy answer if you view it as something innate, it's just a matter of finding the least bad choice. At least if some degree of empathy can be found for the situation you can feel that he could receive 'more help'. EDIT: Although admittedly, I guess empathising with aspects of the event is different than sympathising as you're suggesting.
The idea that it's beneath him woul likely be some part of it, feeling that he is too good to resort to such methods, but it also extends far beyond a mere desire for sex. His issues are deep-rooted. He has a contempt for other people being happiness, and women's rejection of him. This is misogynistic in its suggestion that they should be 'his' as if women are an object, deluded in his feelings of grandeur and inflated sense of self-importance, and an indication of his inability to recognise the emotions of others. If he had a prostitute, it might not conform to his expectations and could illicit a volatile response. If he had a girlfriend, he would almost certainly not have been able to handle the dynamic and shifting relationship that occurs between intimate (again, not necessarily just sexually) two people, and if things worked out poorly, could further enhance the sense of rejection (and his anger would then be directed in a very specific direction as opposed to this broader rampage). Most of this is speculative, for obvious reasons, and deriving from his videos and posts, but he really did need help (and yes, he was receiving it as we now know, but these issues are what needed to be tackled more than his desire for sex). Perhaps it may have taken the edge off him momentarily, but it would have almost certainly been a stop-gap, and could have led to issues festering and manifesting in an altered manner.