Bioshock Infinite - How it should've ended SPOILERS

I get that the whole point of the game was that choice was an illusion and the only way to fully "kill Comstock/DeWitt was to kill him before he even existed and of course the theory goes that drowning Booker before he becomes Comstock "closes the loop" because every Booker is drowned MILLIONS of times over or something like that or the other theory is that there is only one Booker. the point is somehow drowning Booker turns that Baptism into a constant instead of a variable and according to what I've seen and read the reason for that is "just because"

What I wanna know is why? why is drowning Booker more effective than just shooting him in the face in the universes that he actually took the Baptism. why not just shoot Comstock in his million universe faces and let Booker live happily ever after with Anna. and by happily ever after I mean being a murderous raging alcoholic with a major gambling problem and a HUGE debt to pay and is by the way willing to give up his daughter to wipe away his debt which means he as very large debt or he values his daughter very little.

anyways I wanna know why not just shoot Comstock in the freakin face CONSTANTly

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