Our streets and buildings and such were not erected with the idea that anyone can "create art" on them. Street art should be limited to known artists who have been approved, their designs have been approved and their designs better the decor of the city. If street art is open to any individual who wants to do it, it will become overrun and ugly.
Art is art. Beauty is in the eye of the beholder. This being said, do not forget that there is such a thing as destruction of property. Even though many talented street artist have no way of properly showcasing their vision this does not give them the right to embellish the streets with what they think is visually appealing. Their art affects too many people for just these creatives to make the decision of what and where they want to draw, paint, or destroy.
There should be no discrimination on art. Art is art, no matter if a well known artist does it or an up and coming artist does it. If it is good then it should be acceptable. If it is bad it is still art. Art is subjective so there is no staple to what constitutes art.
Street art by any artist that is approved by a city should be acceptable. It does not matter if the artist is well known or not; if citizens of a community find the art work creative, then they have a right to use it in their city. Many enjoy street art because it breaks up the monotony of the concrete and buildings in a city.