imagine seeing Bob and he asks me the question, "How could you marry some one just like the people who killed me?"and when you further worry that
All the reasoning in the world will not help me answer that question from Bobyou are neglecting to draw some vital implications from the irremediable fact that
Bob. Is. Dead.
And cannot pose questions or reproaches.
Whether your daughters do the youthful experimentation bit or not (it's quite possible they will; it's more than likely they will go on to be reasonably happy and functional adults as so many have before; you might want, at appropriate moments, to talk up the perils of driving under the influence of any intoxicant and particularly of riding with an impaired driver), and whether your wife sees the stuff as being negligibly harmful, has nothing to do with Bob's opinions in these matters--he has none; he has not existed to have opinions since the night of his death--and everything to do with your own obsessive projections. This is magical thinking of a type considerably farther out in the ether than the "marijuana is not harmful mindset" you are so concerned about. I am sorry that your personal tragedies have resonated so deeply, but we cannot make social policy just to lay Bob's ghost for you.
It appears that this thread has stirred up some issues within you. I'm no therapist (have you considered that route?), but it seems to me that the time to address these issues is before the Daughters and the Dreaded Drug becomes Topic A over dinner, and before these unresolved feelings cause you to say something truly boneheaded to your wife (I know a thing or about feminine moral accounting, young man, and let me tell you if you haven't noticed already that these debits stay in the ledger a long, long time). This doesn't mean you have to come over to our way of thinking ("Yield! Embrace the Dark Side!"), but you need to be able to talk these things over with your near and dear without the dead hand of a youthful tragedy choking the reason out of you. Make this effort and I predict that you will both avert a measure of domestic discord and position yourself to make a more persuasive case to your daughters when the time comes. Good luck.
cordially,
[edit: duplicate word]