I remember when I first started using clipless peddles, you free the foot on the wrong side, and odds are high you are hitting the ground. Stupid easy to do.
If you're doing some sort of recreational/sport biking, then ya, a lot more people are going to agree you should be wearing a helmet.
Around campus, problems from not balancing with a backpack are more likely.
Though, I do mean to say I don't think it is a certainty. Just that it is more likely than you'd think. And helmets are good at low speeds. They are not just a high speed protection.
Is it a certainty? Of course not. But, by that same argument, seatbelts are useless the vast majority of the time. Indeed, on most moving vehicles I'm on (busses/trains), I don't wear them. Not even offered in many cases. I still support and recommend them where they are available. Same for helmets.