Writing off Plagiarism

Question 3: Is claiming ignorance about plagiarism enough of an excuse? Who's responsible?

At the college level, students should fully understand plagiarism and its consequences. However, plagiarism can be completely deliberate as well as accidental. In the case of the University of Virginia, I think the students really did not fully understand they were plagiarizing. Personally, I think the punishment went too far.
I think many students plagiarize without realizing it. For example, sometimes it is hard to reword a sentence that already is simple and to the point. I think if a student uses such a sentence, but only a couple times without knowing they were "stealing" words, they should not be automatically punished. Instead, if a student is found with this problem, they should be taught that if they use the same wording as their informational source,(even if it's a small idea) they need to cite it. Lots of kids do not understand this. I think it would be beneficial to teach students this to prevent this mild type of plagiarism. I think this is because most students learn not to plagiarize entire paragraphs, which is obviously deliberate plagiarsm. But when a student takes just one sentence, and only tweeks it a little, I do not think they are being deliberate. If being punished for copying one or two sentences can be so severe, I think it should be on the teachers' parts to ensure that any type of copying is plagiarism, whether it's a few words or whole paragraphs.