Of course tickets generate revenue. That's really not the point, though, or at least it shouldn't be. Now, some people like photo radar and so forth, some don't. I can live with photo radar in school zones, playground zones, construction zones, and places where it's not feasible for the police to do speed enforcement. Red light tickets are easy to avoid up here. They only ticket you if you enter the intersection when the light is already red, so you have to be doing something fairly foolish.
As to the other points, what are the school zone hours in Chicago? If school zones are in operation until 11:00 p.m. and on weekends, then it makes sense that the cameras would be I'm not a fan of school zones going overboard. They thought about 24 hour school zones in this city, and the police told the city council directly that they simply won't enforce that. In Regina, our school zones (and playground zones) are 08:00 to 22:00 all week, all year. Years ago, it was only school days for school zones, but that created the problem of what's a school day, when it comes to exams, statutory holidays, teacher conventions, and so forth.
When it comes to children being on school property or playgrounds, yes, 11:00 p.m. might be a bit late. 10:00 p.m. is not out of the question in the spring and summer, particularly a Friday night with kids playing in the school grounds, football field, baseball diamond, and that sort of thing. In fact, I think 8:00 a.m. is too late to start. My high school here started at 8:05 a.m. (yes, 8:05, not 8:00 or 8:15), and kids were obviously converging on the school zone before 8:00 a.m.