I’ll address the points you seem to have the most difficulty with as best I can.
As far as pre-existing pagan religions having the same basis as Catholicism (a son of a god dies and is returned to life), I believe if you look at them carefully, there is always some distortion in the story. If you believe in the Blessed Trinity, then you believe in Satan.
Would Satan not want to plant seeds of doubt in the minds of future believers? A good way of doing that would be to arrange false but similar stories that predated the True Son of God. In that way, people might question the veracity of the Scriptures, as indeed you are.
As to original sin, the Church requires us to believe that there were two original humans into whom God breathed a soul which was in His image and likeness. We are free to believe in a six 24 hour day creation or development of Homo sapiens over the span of milion of years, as long as we believe the immortal soul part.
These two were born with glorified souls. God gave them only one command, which they violated. Thereafter, the soul God gives to each of us I percieve as being “mutated,” if you will, by their act. Jesus came to rectify that mutation, and did so perfectly.
Whenever a little worm of doubt wiggles its way into my faith, I put this question to myself:
If Jesus Christ was a phony, if he didn’t actually die and rise again, why woud the Apostles do what they did? They saw His brutal suffering, the Roman torture and the agony and death on the cross. They were there.
To what advantage did they preach the death and resurrection of Jesus christ? Did they expect earthly wealth, power or fame? For what possible reason would a man knowingly and voluntarily preach a story if he knew doing so would result in his painful and violent death, most likely preceeded by torture and humiliation unless he knew it was the Truth. Because, if it was the Truth, he’d better preach it, suffer for it, die for it, because eternity never, and I mean never, ends.
In the history you’ve read, have others voluntarily died for a lie? Did they gladly die for what they believed to be the truth?
And this is NOT the same as war. In a war, one doesn’t expect to die, and one fights and does not submit gladly to death unless he does so in order to save his comrades.
“No greater love,”
That’s the best I can do, my friend. I decide every day to believe, and so I do.