The problem is that Christians can't even agree on what god does and does not consider a sin; even though they're all working from the same text, they all have vastly different interpretations on what it says, and like to pick and choose which parts they believe in. It's one of the reasons why there are so many denominations. Some would argue seeing a doctor is a sin; others, that using any technology more advanced than a horse-drawn carriage is a sin. Heck; I've read the Bible, and I recall seeing a passage that proscribed crop rotation, though I couldn't quote it to you. Then there's the prohibitions against shaving your facial hair and eating pork or crustaceans; things most Christians agree they shouldn't treat as sins, even though it's in the Bible that they are.
As for homosexuality, the only part I've been able to find that specifically denotes it as a sin is in a direct quote from Paul; so that may have just been his personal opinion. Everywhere else in the Bible, in the parts that most people quote as evidence for why homosexuality is sinful, it's specifically talking about sodomy being a sin, NOT homosexuality. In other words, the act of sticking your dick in another dude's mouth in and of itself isn't a sin, according to the Bible, but putting it in a woman's butt, is. Unless of course you take the view that any sexual act that doesn't result in pregnancy is sinful, even if you happen to be married; and that marriage can only exist between a man and a woman. Neither of which every Christian believes.
You hit on a good point 'Christian Conservatives' like to...leave out of the arguments related to the Bible, and sin, and that is the fact there are so many versions, so many different offshoots, and so many blatant contridictions in the text that.
Look, historical fan fiction is a nice way to put it.
There was probably a guy named Abraham who...I'm not really sure how much has been independently verified by other historical sources to have been actually done by him, rather than attributed to him.
The Flood myth was probably a twisted telephone game retelling of the opening on the Aegen Sea into the Black Sea in pre-history, mixed with both Nile and Tirgris/Euphrates flooding events.
I think the Sodom and Gamorrah story was a parable crafted from a survivor's story about a meteor airburst over part of the Dead Sea area where some trade hubs were, that happened to have all the normal debauchery towns like that had in that time. They've found trinitite samples in the area, and the only way to make that mineral is with either meteor hits or nuke groundbursts, and there's no abnormal rads in that area.
The Plagues of Egypt were likely the result of a series of volcanic eruptions in the Med and Cameroon fucking with the weather, spewing invisible clouds of poison gas close to the ground in some areas, and causing a cascade of environmental disruptions.
The whole 'wonder the desert for 40 years thing' after they found that town, and decided not to attack, and was probably the Hebrews just building up forces to make the attack work, as it could give them another 2 generations of bodies to field while they kept an eye on the target.
There probably was a Jewish dude named Jesus who lived around 1AD, who lived in what is now Israel and Egypt, who ended up with a following when he started cleaning house at the Temple, who defied the Romans as a messianic figure leading a local rebellion, and got crucified for it. His followers survived and rallied in his name, working underground to keep the group alive and recruit new members, till Justinian made it state religion after winning a battle after he supposedly prayed to a cross shaped image in the sky. Then it kinda snowballed from there, with early sects that were 'heretical' to mainline dogma/political desires splitting off and infighting occurring for a while.
That doesn't even count the whole 'stealing pagan symbols and rituals to gain converts' bit that many Christian sect have done, the Christians who decided that the Bible said it was ok to enslave their fellow man, just because he had a different skin color.
All of this feeds into why we must have secular laws, and not let any religion dictate public policy. Because no religion has a monopoly on historical truth, moral superiority, ethical behavior, holiness, or righteousness.