If we decided that art could only be produced by 'experienced professionals', using 'expensive professional equipment', and must be 'meticulously planned', the world would be a far less interesting place.
And then after the fact, are reacting this way. They're not shooting for a project, to build their portfolio, etc. They simply took a picture of something they saw.
If we're talking about amateur stuff that gets thrown out at random, that's cool. But I'm not sure that putting well-appreciated art and random amateur art in the same category is a constructive argument. Like even all the really good Youtube artists who are hitting it big these days go bling bling on equipment and put a ton of effort into their work, and they're getting paid via Youtube ads to boot.
It's also one of the most influential art pieces of the 20th century. It, and his "found art" movement in general, are the cornerstones of the redefinition of art and mark the invention of conceptual art. Art no longer has to do with who made it, or how, or how much effort was put in. It's about intent. If you buy a pencil and say it's art, it's art (if perhaps not very good art).
http://en.wikipedia.org/wiki/Readymades_of_Marcel_Duchamp#Do...