If it makes you feel better, I don't blame you for the shooting, and I am pretty sure that if you had stood up to every person who made a racist joke, and written letters and emails to every TV company that featured something a bit racist, or denounced politicians such as Pauline Hanson and Fraser Anning, this event
still would have happened (notwithstanding the vagaries of chaos theory).
I know that whenever I have said, "Hey, that's racist!" I have more often been met with derision or "So ******* what?!" I think calling it out is not something that tends to be successful.
I think there is also a problem with this self-imposed collective guilt. It has corollaries that you probably don't want to make.
Isn't it common to hear people saying such things as "Muslims need to denounce terrorists who commit terrorism in the name of Islam!"? Would you agree that calling yourself guilty of this crime by virtue (or vice) of being a white Australian, it also suggests that Sunni Muslims should feel responsible for the atrocities of al Qaeda and ISIS? Or that Shia Muslims bear some responsibility for Hezbollah? Or maybe Irish people bear responsibility for the IRA, and Japanese people are collectively responsible for that
Pen, Pineapple, Apple Pen song?
It's one thing to argue that action should be taken against racists, and that people should vote out or shun racist populists, but it is another thing to say
you are guilty! In fact, trying to share the guilt around is almost exculpatory of the actual murderer.