You and I are pretty much in agreement. What you just wrote is basically how I feel as well.
I just object to the reasoning many in this thread have used for their position against graffiti because I agree it's not black and white. You can't argue LNT when the shelter itself is a violation of LNT premises. It comes down to a personal, subjective opinion. For me personally it's neither offensive nor a violation of any moral/ethical position.