Is The Really Art Or Defacing Public Property?

I literally stumbled into the "artwork" under the 5th street bridge. I was investigating some in town Colorado river access points when came across the graffiti on the pillars. I also know I'm not the first here in our Townsquare Media cluster of radio stations to post some thoughts on the "artwork" or "graffiti." What you call it, well that depends on your point of view.

I must admit, I have respect for the work. Taking a can of spray paint and creating cool graphics takes great skill. I could hardly spray paint a couple end tables I picked up at a local garage sale without a couple runs down the sides.

Again, I'm not an artist or musician, but as a lover of the two mediums, I do appreciate the hard work and dedication that goes into creating a work of art. The question is, Is this an appropriate place to express the art form or is this simply defacing public property?       

As my colleague noted in his radio station post a few months ago, I too mistook the message "Art on the bridges is a gift, thank you GJ, CO" to be some type of endorsement of the activity by the city. I too couldn't find any such thing. Also too, since the work in under the bridge, and not in plain site, does that make it acceptable? One more thing, if the city spends the time and money to paint over the colorful works, is that going to clean it up or simply provide a new canvas for the next spray can wielding guy or gal?