Why are people against graffiti?

I have one neighbour who only graffiti's my buildings. They will tap nothing else. This causes my five stars (that I sweated and slaved to get) to drop really frequently. Fortunately for that person I am not that bothered really about my Conformometer but I have had to place dozens of Training Walls to counter their attacks. It has got boring. I got bored by it about a year ago. However what they don't know is that they are the only neighbour I have who I NEVER help during events. I won't drop them though as I value daily players and even daily sprayers. It all adds up. I only drop neighbours who haven't played for more than two months.