Mortal sin is mortal sin. We are supposed to grow in holiness, not to feel comfortable in our ignorance.
Ignorance and deliberate consent are diminishing factors after the question as to whether negligence exists.
The question of due diligence in knowing what the Church teaches often means that a person is voluntarily responsible for their actions. I’ll admit, there are cases (not some) where reasonable due diligence is impossible, but they are not that often though in a society with the access to information we have.
One cannot simply reject the teaching of the Church because you don’t understand it, and expect for that to be a diminishing factor. The law is difficult because it is mean to teach us, not to engage in legalism. The Church has authority to teach us because it comes from God who we must obey, not just because, at that time, we think it is a great idea.
This is because, understanding comes to us often after doing a thing. Children have to be taught this way. And we are children to God.
I am reminding myself to give much more emphasis to