Well, they can't all be about terrible tragedies and giant mecha battles, can they? There needs to be a few to establish the characters.
Although, I also have mixed feelings about this chapter. It seems pretty explicit that there was supposed to be a moral to this story, however I can't decide if it's supposed to be the "forgiveness is the best policy" or the opposite. The way the characters present it and the whole where the crazy old guy gets hurt and they discover that he didn't really have any bad intentions would suggest that the moral is for forgiveness, but that doesn't really hold up if you think about it for five seconds. If they had called the police immediately when they found out about it, then they could have just caught him when he broke into their house. He also had already done that before and was going to do it again. Better that he get caught then so no one gets hurt in the future. Besides, the only response that I can come up with to the idea that calling the cops when your car gets jacked is immoral is "wat?"
So, yeah, it's probably that forgiving people indiscriminately is irresponsible. Or, perhaps, more likely, it's "forgive or get revenge, but whatever you do, do it immediately and don't be wishy washy about it." Yeah, that makes more sense, especially taking the last few chapters into consideration.
Then again, I'm just over-thinking things, and the only purpose to this chapter was almost certainly to establish why Chizu listened to her sister last chapter. This isn't the type of manga to have absolute morality.