Of course.  But lets be clear, ignorance is not a good thing. Satan is called the prince of darkness for a reason.   We are to bring the Light to the world that is in darkness.  

We are obligated to seek truth and follow it!  We are to know the teachings of the Church and spread this truth through evangelization.  Remaining willfully ignorant or allowing someone else to be ignorant of a sin to avoid culpability is in itself sinful. 

Sin is always a bad thing, regardless of culpability.  If someone is contracepting when ignorant of the Church's teaching that it is wrong, they may not be culpable and will not be held liable, but it is still an offense to God and we should help those ignorant of a teaching to know the truth.