Plagiarism

i was accused of plagiarism my freshman year in high school because i was the only person in class who worked on the assignment instead of watching the superbowl the night before it was due.  how is that fair?  we are requested to submit our papers to turnitin.com which to me is just a slap in the face.  many professors don't give their students the benefit of the doubt but instead assume they will plagiarize until a website says they aren't.  there is a reason why our justice system is founded on the premise of innocent before proven guilty, why doesn't the world of academia follow suit?  the argument that students plagiarize so they HAVE to use systems like turnitin.com is bullshit.  just because SOME students plagiarize does not mean that i do nor does it mean that you should assume every student is guilty of such until a website justifies our claims of innocence.