@Chely4554,
School is an institution where people learn a skill set that they can use later on in life, particularly for a job. As such, plagiarism is a serious issue: it means it becomes impossible to actually measure a student's acumen and/or knowledge in a particular field, since they are being graded for work they did not do themselves. Allowed to continue unchecked, this means that people might be able to graduate with a diploma that implies they have mastered a number of disciplines that they have, in fact, not.
So it's a serious and hard no. That being said, the impact for doing something like internet plagiarism should be dependent upon the institution it is committed in: in elementary school, I'd say that a serious talk and warning would suffice. In junior high, an immediate warning and a slashed grade perhaps(an automatic D or F for the paper that was plagiarized). In highschool, a serious talk, having to do the paper in question over (on a different subject perhaps), and with a repeated offense, failing the course, detention and/or expulsion.
At college or university level people really should know better: Fail the course, make a note for other teachers to check the work of said students extra diligently. At a repeated offense, fines (if possible) and/or expulsion, as well as a failed course.