I recall Jesus saying that, if someone led another into sin, the first would be punished severely but the second not so severely. So they would still face punishment. (Don’t remember scripture/verse Also, Paul writes that we have no excuse for not knowing God as we need only look around and see proof of Him. (That’s in Romans somewhere, sorry can’t quote verse)
I think the bottom line is that, if we know what God expects of us and we don’t do it, we can’t really say that we love God. We should be forever striving to serve Him - to become saints.
Some people choose violence and justify it with religion. That doesn’t mean that they don’t know what is truly right. That’s not to say that some aren’t “brainwashed”. Consider those who might be naive and are caught up in “religious feminism”, worshiping Goddesses and participating in “white witchcraft”, rejecting God the Father for God the Mother. Some people know better, others are tragically misguided. God knows the difference - he knows people’s hearts. Just because someone quotes scripture doesn’t mean he is serving God. Think of Satan - he knows the Bible!
Follow God and do right because it pleases God, because you know it’s the right thing to do, because you want to be holy and perfect when you come into His presence in the next life. Don’t worry about whether it’s “fair” for someone to be able to sin out of ignorance. Be grateful that you know what pleases God so that you can be more pleasing to Him. Focus on Him and all will be good.