Hmmm... well I don't think I would considered a plagiarized piece of work Art, guess it depends what we are talking about. Art certainly draws upon influence and inspiration, occasionally it can be revolutionary as well.
Or preversion. But all kidding aside, it is revolution. A great artist must be a provacatour, so to speak.:afro:
By plagiarism I thought people copy emotions like joy,sorrow... expressed in art. however, there are also profound,,deeper and unique feelings.
Music is my main experience with art as I listen to it daily as well as play guitar. So with that in mind, I'd say humans respond to particular notes, chords and melodies that evoke those emotions you listed and others, so as a musician you have a limited number of ways to express yourself through the instrument in music, especially if you want the music to be rhythmic. Then take into account and include the musician's ability to play the instrument and influences as well and many people's music may start sounding similar. I'm not sure if other art forms are bound to a lot of limitations as well but I'd assume so.
art is what makes us human. it is part of everyone. all creatures explore. 'humans', that is to say, the dominant sentient life form of every world that has one, are born to create as well. plagerism implies an intent to deceive as to one's source. to take credit for what is not their own. i don't agree with that part of the op. i think everything, comes through us, and because there are so many of us, it is inevitable that it sometimes happens that the same inspirations flow through many at the same time, with the occasionlly uncannily similar results. this is not nearly so important as it is, to let imagination flow through us. opposing its flow, buying into cultural values that do so, that is the real source of mental instability.