It is not acceptable behaviour.
Anyone teaching at an institution of higher learning will tell you that "copy-paste" term papers are pretty par for the course. The students claim that they are overworked, don't quite understand what is the objective of the paper (and hence stuffed everything possible in it in hopes to garner some mercy points) and all kinds of excuses ("I didn't have time to do the paper properly since my cat died and I'm in mourning." is my personal favourite) to justify their action.
Identifying plagiarised paper of most student is actually pretty easy; just look for islands of flawless sentences in a sea of awkwardly written prose or perfect English sentences from students who could barely identify themselves in said language. Softwares like turnitin makes proving academic dishonesty that much easier.
What are the consequences of citation amnesia? It ranges from suspension, paper retraction or to even stepping down from being the defense minister. Karl-Theodore zu Guttenberg, a charismatic and youthful politician from aristocratic lineage (with the courtesy title of Baron), was alleged to have plagiarised significant portions of with Doctorate of Law thesis. Four years after granting him the degree, the University of Bayreuth withdrew his PhD.
The moral of the story is: If you lie, don't get caught.