There are three people, each of whom has committed a deed that is bad, yet in worldly terms advantageous.
The first person has not realized that he committed a bad deed and goes on acting the same way.
The second person has realized that the deed is bad and no longer acts that way.
The third person has realized that the deed is bad, yet goes on acting that way nonetheless.
If someone from the outside says that the deed is bad, then the first person will be surprised, the second will agree, and the third will argue louder than anyone that the deed is not bad. If, in the end, one manages to break the third person's reasoning and he has to agree that the deed is bad, then he will try to taint the first and second person, saying they too committed this deed and deserve no less censure.
However, I believe that greater censure is deserved not by the bad deed itself, but by the attempt to whitewash it. The attempt to whitewash is potentially very harmful, because in the long run it allows a greater number of bad deeds to be wrapped in the guise of worthy ones.
All three people are guilty, of course — they all committed bad deeds, but the third is also guilty of lying.
Yes, committing a sin out of ignorance (the first person) is always less sinful than doing so intentionally (the third person).