I have a question on culpability…
If someone before knew something was a big sin, yet committed it without even thinking (not thinking - ok, I know this is wrong; I know it’s serious; I will do it anyway), but was thinking later on, “oh wow, that wasn’t right.”
How guilty would this person be?
I think that you have to look at the surrounding circumstances.
Let’s take impure thoughts. They are a big sin, and pretty much everybody knows they are.
But there are times during the day where we start entertaining them without even thinking. When we realize we are doing this we stop, and are guilty of committing a sin of grave matter, without full knowledge…aka venial sin.
Full knowledge for mortal sin is basically asking, “At the time, did you know you were doing something grave matter?”
Of course, there are some times when we SHOULD know that we are doing something of grave matter, but are responsible for not knowing. For example, someone who doesn’t think contraceptives are sinful purposefully tries not to read an encyclical about contraceptives, knowing that the Pope will most likely condemn their idea as sinful.
They technically don’t “know” it’s sinful, but still are culpable. (and also they are heretical, but that’s a whole different subject matter, involving excommunication)
Or another example: a worker who should have read the manual for how to repair a faucet chooses not to, out of laziness. He absolutely wrecks the faucet, out of his own fault. He would be more culpable than a worker who makes an honest mistake; the former would be guilty of mortal sin, the latter, venial, or even no, sin.
So it’s not clear-cut black and white.