I guess that means you don't have a problem with students turning in work they've cut and pasted directly off the internet?
What if the student writes an opinion in a paper, and later in life, when his opinions and views may have changed, this former opinion is held against him when he goes to apply for a job? Have your views and opinions changed since you were in high school? I know mine sure have. That comes with maturity as well as with experience.
One of the big problems with today's society is that we want everyone to be perfect and follow all of the rules, as well as to put systems into place to ensure that the rules are followed. While ideally we should all should strive to be model citizens, pragmatically it isn't going to happen, since we are humans. There will be a few that try to break the rules, but the majority that follow the rules shouldn't have to bear the burden for those that break them.