We are responsible for our own actions, first and foremost.
First and foremost, this is a lie. A rather horrific lie, at that. It denies civilization's ultimate purpose - the ability to anticipate and mitigate circumstances like these, and worse.
If someone is mentally unstable, it falls, ultimately, upon society to pay that price. It can pay a price to prevent a tragedy, or it can pay the price -of- that tragedy. Since deinstitutionalization, the US has gone the route of the latter, at least with those cases. Your line of thinking tells the victims 'oh well, it happened, it wasn't worth it to prevent your friend's macing, assault, rape, or murder'.
We are beings of emotion and instinct, and it's quite feasible to plan and account for erratic behavior. We even have these horrific things like regulations to help plan for worst case scenarios, like oh, maximum occupancy limits. Hell in Saint Paul some restaurants have it electronically enforced (not well, but still).
Which is probably what it's going to take for this to become actually addressed. A very preventable disaster happens, a lot of people die, and finally the political will exists to fix it.
The person responsible for the pepper spraying is the person who brought the pepper spray to the store and used it.
And yet if an arsonist takes down a store which was found to have massive fire code violations, thus escalating casualties, the store will be found to be responsible. Is that 'wrong'?
If I let Elliquiy's server get hacked, I am in part responsible for the damage my server does to other servers, as well as Elliquiy's visitors, both legally and morally. Who would you blame if visiting Elliquiy infected your machine, 'just' the attacker?
When Steam got hacked, did they 'just' blame the hackers? They apologized, and for good reason.
You have a public place, you have some measure of responsibility for what goes on with it. I disagree with the government where that line needs to be drawn, but it does need to be there, even for the Internet. It simply would not function otherwise.
This is a very common, and distressing line of thought. Deflection of responsibility.
I find your line of thought far more distressing, if only because many policy makers currently think like you do. And they see the logical end-conclusion of it, but because they think like you do, they don't see an alternative to what they see as an inevitable biological holocaust. One of them told me, flat out, he doesn't expect humanity to last another fifty years, so why plan further?
...because blaming it on 'just the perpetrator' denies society's capacity to prevent an omnicidal maniac from doing it in the first place.
That is a cop out. The coward's path. Or short-sighted sociopaths.
Like the same people who try to blame 9/11 on anyone but those people who flew the planes into the buildings.
You play the game where you lose 100 people to their 1, I'll play the game where we don't lose any. Who will win, in the end?
I am responsible for my own actions. I am not responsible for anyone else's. Period.
You antagonize someone into attacking you, and your antagonism gets witnessed, you may end up being the one charged. It's the 'fighting words' defense.
Similarly, you refuse to contribute to society to provide such security (reinstitutionalization, for one example), you have that much more of a chance of eventually paying the price - or someone you know and care for does.
Unfortunately, that time only exists in fairy tales.
Measures of empathy do have correlations with various societal trends. Despite various groups trying to sing its praises, sociopathy is not the societal norm. Most humans are naturally inclined to care for each other, as a matter of reflex. It's only when stressed that they start thinking of themselves first. This is a natural response, but when over half of our productive output is going to security in various fashions (including legal), something is in fact very wrong.