I'm sure a lot of people would agree with it or disagree with it depending on the wording of the question. People here are totally willing to agree that God controls everything and that everything is his will, although they're silent when a relative dies or someone gets into a car crash...
Right, but the fuss over the guy's comments isn't about the theology.
"It's all part of God's plan" isn't meant to be taken as saying that the thing that's part of God's plan is a good thing. The idea is that God's overall plan is a good thing - to make an omelet you have to break a few eggs. You hear it when someone dies unexpectedly, for example. It's a Job thing; things seem pretty awful, but God will see to it that everything works out in the end (possibly in the afterlife). But things still suck now, and nobody's minimizing that.
That's not what Mourdock was doing. He was pretty clearly
not counting the rape as mysteriously part of God's greater plan; he's not trying to express compassion for rape victims. He's
telling rape victims that if they get pregnant they need to regard that pregnancy as a good thing. It's not just "whatever happens is part of God's plan"; it's "you carrying this rape baby to term is part of God's plan and you better not try to change that". There's an enormous difference between saying that something that's already happened is part of God's plan (reassuring) and saying that someone has a duty to follow (what you think is) God's plan (authoritarian).
Edit: To be absolutely clear, the non-offensive use of "it's all part of God's plan" could be applied to the pregnancy, but also to the rape, and also to the later abortion. That's not how Mourdock's using it. He's since clarified that, yes, he really did mean it in an authoritarian way. Biology isn't random and so God specifically chose you to get pregnant, so you can't go against that.
Edit2: So I suppose I should also be explicit that I don't think it's fair to say that people stop talking like this when a relative dies. I don't think I've ever been to a funeral for a not-ancient person where the clergyman didn't talk about God choosing to call the person to Him. There's typically a lot of talk about us not understanding the reasons for that, but having faith that we'll all be together again later on.
