Comment on Is the Editor of the Springer Journal Scientometrics indifferent to plagiarism? by Bill White

The question I am posing in regard to this issue is (or similar issues): would it be FAIR to penalize an author for 1 or two sentences, one or two paragraphs he/she copied? He/she may did it with ignorance, without knowing about plagiarism or simply because he is novice.
What is the true or concrete implication of such issue?
I think that an author who copies on another author (without citation), he does it undoubtedly by ignorance or incompetence, otherwise he would not not do it.