It's not just the raisin. It's that they're slipped into delicious items surreptitiously. I swear that people do it as a prank.
Cinnamon rolls look, and smell amazing. Bite into one and expect a pecan but, instead, get that squishy ball in your mouth and wonder if a fly fell into the batter or if the cook is a jerk.
I've bitten into cookies of all kinds with those little rat turds in them and wondered out loud Why!?!
The worst that I can remember was a carrot cake. Why ruin such a near perfect confection? I bet that all of the religious turmoil in this country began when the baby Muhammad brought the baby Jesus' favorite dessert to the first Thanksgiving (carrot cake). Jesus probably bit into a couple of raisins and it was on!