I may as well use spoilers as well just in case.
(SPOILER)I don't see it as in bad taste necessarily. Is the thought of mowing down innocent civilians horrific? Of course, but I'm pretty sure that's what Infinity Ward is going for. They didn't shy away from putting us in the middle of televised executions and nuclear fallout before. Both were horrifying moments that were presented in such a way that it really made you feel at least some of what it may feel like to be in that position. It's horrifying yes, but making people realize that is part of the point because crap like that happens every day in many parts of the world. I see it as Infinity Ward sort of putting the player in the middle of it to make a statement: that this stuff is terrible and shouldn't happen or be ignored ever.
GTA features violence for the sake of entertainment. It's supposed to be fun because you can do whatever you want consequence free. Infinity Ward is showing the more horrifying reality of such violence though. It may not change how you feel, but if you find it appalling then good. My bet is that that was their intent.