There are potentially millions more "elliot rodgers" out there.
This is not an isolated instance of the plethora of negative and unfavorable conditions, to which he was involuntarily and inevitably, and most importantly, ceaselessly, exposed.
You push ANYONE hard enough, far enough, for long enough, they WILL snap, regardless of your opinion of their reasoning/motivation.
You convince someone that all they'll ever be allowed to experience is various versions of unending torment... they'll say "F*** it!" and behave destructively... because why would anyone try not to damage a world (or its inhabitants) that has ALWAYS damaged them? (this is partly a perception and subjective, individual experience issue...)
I've been to that same edge myself a few times. I've even been close enough that, had i possessed the means to make a big enough "dent," i'd have used them. Luckily, i've always struggled with the long term impacts of an insufficient earning potential, due to the decisions made by others, for themselves, which lacked the consideration of how those decisions (by others) would negatively impact my environment.
We are all products of our environments; the only way you can shift the ratio enough to have "control," (i.e., to choose one's own life parameters), is to be able to amass enough resources to be able to control other people's actions/decisions, or alternatively, remove them and their impacts entirely from your chosen environment.
"Do or get done." If you can't control what's happening around you (including other people), then you will be exposed to whatever your environment ends up putting on you. Sometimes there is no way to gain control, and no way to escape.
Instead of fixing that problem, people want to cry "monster!" ...even though, yes, our society "created" such a monster... and he's absolutely not the only one. There are many out there, right now, just waiting for the last straw to land on the camel's back.
I feel sorry for the dude, and his victims. I don't think he "deserved" the life that pushed him toward his actions, and i don't think his victims "deserved" to pay for what he couldn't handle.
The whole thing just sucks... but that's pretty typical for Earth and Humans, from what i've seen.