There is no excuse for plaigarism, and it is a problem for two reasons:

1) In this day and age it is easier than ever; and
2) even though you can do a quick check in a search engine to see if something is blatantly ripped off, it is not happening regularly enough to deter people from copying stuff.

At my uni if you get busted for plaigarism, you get kicked out, no exceptions. This sort of attitude along with more stringent checking by those people who mark papers would result in people taking plaigarism and copying more seriously.