No consideration for how their actions affect others?
Lack of spiritual or civic education?
Poor parenting?
Immaturity?
It just struck me that this is similar to a problem I encountered over the summer.
I was tenting in a campground for a week. Everything was fine, I was enjoying the peace and quiet, then the weekend came and some younger people set up across the road. Next thing I knew there was loud rap music blaring out something about bitches and asses. I wasn't going to put up with it and went over to talk to them. They were a couple of youngish women. I told them I really didn't want to listen to their music and received the snarky reply from one, "Well, don't then". I told them that was impossible at the volume they producing. They said they were allowed to play music to 11 PM and I replied that excessive noise was not allowed at any time, that I had no desire to argue with them and if they didn't turn it down we'd let the park rangers decide and returned to my campsite. The music was turned down and a half hour later they came over (after they had gone and talked to the ranger) apologized, agreed that it had been too loud, that they would keep it down and offered me a pair of ear plugs. I looked at the earplugs with a degree of incredulous astonishment but graciously accepted them.
Point is, how could somebody be so inconsiderate,so uncaring, so braindead to think that blasting their music was their right regardless of the presence of others? The answer to this is probably the same as the answer to your question.
WHen you mix the same attitude that you observed with in -your-face dog ownership (and yes I know that not all dog owners are irresponsible, but a lot are) then maybe you begin to account for the hundreds of thousands of serious dog bites every year. Now what to do about it. At least the idiots with the music were not likely to physically injure you with their music. Too many agressive dogs, a..hole owners that are proud of the fact that their pets can and probably will cause harm to someone, and the general attitude that dogs can do what they want needs changing.