The ability to actually paint or draw something is fairly irrelevant in modern art. Technique can be taught and honed through practice.
Hirst and many others (Chapman bros, emin etc) regard themselves much more as "conceptual artists" where ideas are currency.
Much of Banksy's work could also be carried off by you and me but what I love about it is the subversive and satirical nature. He also made it accessible to the public and to an extent democratised it by taking it out of the so called elitist sector of galleries and museums.
This is all personal opinion and I am in no way an arts expert but i do have some experience of both the modern art world and visual culture.
I don't however have a collection like some (you bastards!) as I have rarely had the spare notes to consider it and would rather hide behind the pretentious and poncey line of; art can never be owned.