Yes, in a world where we are bombarded with the need to conserve energy; which is changing the way we produce, deliver and use energy to complete the daily tasks we take for granted, such a frivolous waste seems difficult to justify. The climate change debate may rage on, but it is undeniable that poor use of natural resources is having a detrimental effect on the lives of people across the world. If a small improvement in the conditions for people on the planet can be made by not lighting up the skies then I think it is a cross we can bare, and personally I find it difficult to beat nature's own light show on a clear night. Why compete with the stars, when we could never hope to match the power such a display involves and the awe it inspires?
It's the same reason I have a problem with Christmas lights. Nobody seems to care about how much energy they waste by place up these horrific displays of wasted energy. If the lighting serves a purpose other than looking pretty by all means we can keep it around, or if it can be powered by solar powered it would be fine.
Lights, TV, computer, video games, air conditioning, electric stoves, etcetera etcetera. So you waste your precious energy on the internet posting about a light show when there are other non energy using things to do to waste your time? Everything that happens requires energy to do so. If you feel it's worth it then you will do so. Look at make-up for example: Time is something you don't want to waste yet women spend so much time using make-up yet you say nothing about it "wasting time and should be banned because it is only for aesthetic purposes."
There are lots of everyday items that use energy for aesthetic purposes only. You could make an argument for getting rid of heat and air conditioning because we could be using wood burning stoves and fans which would use considerably less energy. This would lower our quality of life dramatically and therefore I don't believe it is a good argument to get rid of something just because it's used for aesthetic purposes.
No, we should not ban light projection mapping, just because it uses energy for aesthetic purposes, because art is important. It is true that art takes energy. But art can also heal the soul. Art can be a politically argument that helps make the world a better place. Art is worth the cost.