(Note: I am not naïve. I would put the chance of getting through to someone planning another attack at near zero. But if, miraculously, one person changed their mind, that would obviously be worth any attempt. So I must try.)
I'm not going to ask you to change your ideology to my own, or ask you to understand my lifestyle or experience. You are contemplating treating your personal resentment and anger in a way that is so foreign to me that the gap between our thinking is unbridgeable. If you have gotten so far as to be planning mass carnage on those who have done nothing to harm you, you are operating from a set of principles that are beyond my understanding. I will not find the words to reach you using any traditional political or spiritual arguments.
And yet, I can find things we have in common as human beings. We were both born to a mother and a father. We almost all have a least one brother or sister, or several siblings. We have cousins and aunt and uncles and husbands or wives. I don't have children but, as we saw in the San Bernardino shooters and in Orlando, you may well be a father, or even a mother.
I don't ask you to consider the families of the victims you plan to kill, even though you should. Clearly, in ways I cannot fathom, you consider their pain an equalizer to your own, a form of justice, a sacrifice to a God I cannot even conceive of.
But I will ask you to please imagine the life of your child. The loss of you as a parent will be the least of it, because if you are planning to commit this thing it is very hard to imagine you have the necessary qualities to be a good one. But surely you can conceive of him or her at six or seven, when the first whispers among classmates result in questions that your other surviving relatives will have to answer. If they do not, the child will go to the internet. They will find out who you were and what you did, and it will be as brutalizing as the worst beating they could ever receive and still survive. You will have defined their entire life by the act you are planning to commit.
Even though you seem incapable of imagining the love others have for their own children, I believe you are capable of loving your child. Like all parents, you want them to have a happy life. You are about to destroy any possibility of that eventuality. You are, in essence, killing your own child along with the victims of your bullets.
If you do not have a child, then think of your mother, your father, your siblings, your aunts and uncles. Read about the experience of the families of mass shooters. You will find out about lives plunged into a hell of guilt and remorse from which they never recover. They are often shunned, and have difficulty finding places to live. The younger ones -- the nieces and nephew and cousins -- grow to hate the shooter. Every relationship they attempt to have is poisoned by the secret they can neither keep nor bear to share.
You won't be leaving your pain behind, but bequeathing it as your only legacy.
If the relief you feel when you fantasize about committing this act involves imagining you will be able to "see" the effects of your act on the society you have somehow decided is your enemy, then realize that will also be able to "see" the effects of your act on your family. Do you think you will be able to enjoy the glory of martyrdom, when you "see" from this otherworldly dimension what it's like for your first-grader to find out you were a mass-killer?
If you are not operating because of political ideology but from personal grievance, you probably fantasize about no afterlife at all. You want your pain done. For some reason, suicide alone is not sufficient for you. Others must know your pain. But if you believe that death is but a void, then you need to realize that you will not even be able to witness the after-effects of your deed, either. You will be dead. And if merely imagining it brings you relief, that relief is still available to you without acting on it.
If you cannot imagine any other relief than that which comes with death, then perhaps taking your life is the only thing that will end your pain. As a suicide survivor, I know how hard my brother's death was on the family, but we had the solace of knowing he was no long suffering. No such solace would have accrued to the other families, had my brother, God forbid, been the type of person who took other lives as well as his own.
Whatever your motivation for planning this act, I know you are angry. You may be angry at women, at gays, at infidels, at military oppression, at being bullied -- any number of reasons. And even if somehow my appeal to your love of family has reached you, that anger has not evaporated. And you don't know what to do with it.
I have a suggestion. Create something. Draw, paint, play music, write. If these activities don't appeal to you, then make a garden. Go and plant a tree for every person you were considering cutting down. Nurture nature, something unopposed by any ideology - no matter how radical. Make something. But please, please, don't unmake the rest of us. Don't unmake the lives of those you love.
And if you believe you are operating from God's Will, have the humility to realize that you cannot know the mind of God. Murder is far too irrevocable an act to risk believing you do.