Saying what is permissible and matters of morality

I saw in several columns that you think a person who is convinced that he is doing a good thing, even if he actually does something bad, will not be punished for it because he is being unreasonable in his opinion.
In the Gemara on Beatings, there is an issue regarding saying “permitted.” They disagreed about whether it is close to intentional or close to rape. And the halakhic ruling is that saying “permitted” is close to intentional, and therefore the Rambam ruled incorrectly that he thought it was permissible to murder a person who is guilty of death. He had to learn and he is not raping.
Does this paragraph agree with what you said?
I suppose we can divide between different situations or different commandments (obviously there is a difference between murder and the details of Shabbat laws), but in general, isn’t it correct to say that in many cases, rape in opinion is not rape?
Moreover, isn’t a person who knows that many people are sure that it is forbidden, and for his own reasons decides to disagree with everyone and do a forbidden act (like Yigal Amir, who wrote that he is not ‘evil’ in your opinion) even more deficient than an ordinary person who says it is permissible but doesn’t know that for most of the world it is forbidden?