english writing

Yes, I understand the concept. A man could have a worthy goal of sending his child to college, but robbing a bank to do so would contradict with his conscience. I would make a slight change to the first sentence. In general, if a goal is really worthy, we should try to attain it by any reasonable means.
The next two sentences are not yet clear to me. I don't know if they refer to the goal or the means to attaining the goal.
If there happens to be a contradiction between two kinds of principles, one being the goal ( and the means to attaining the goal), and the other is our own conscience, which do you prefer to follow?

Does the end justify the means?

Thanks a lot!