Why does God allow controversy?

Christians arguing drives me mad. That reaction is partly righteous because unity brings blessing, and partly unrighteous because I can be tempted to think that everyone should agree with me. Given how inexperienced and immature I am this is an awfully ridiculous thing to think.

These words from Wayne Grudem in response to a question about why God allows controversy are hugely encouraging, and a rebuke to my simplemindedness:
