Ask anyone who knows me, and they will probably tell you that I don't ride in sandals or flip-flops because I never wear such footwear. That is, in essence, truth. But, this is one of the reasons I don't wear them.
When we were kids, my sister was either barefoot or in flip-flops for most of the summer. She always wanted to ride her bike barefoot, but our mother wouldn't let her. So, she rode in those old-school rubber flip-flops that some people call "shower shoes".
One day, not too long after my momentous removal of the training wheels, Joy and I were riding on the Dead-End (we never called the street by name, it was the Dead-End, not a dead-end, if you know what I mean) and we decided to drag race. Joy was 2 years older than me, and a bit bigger at that time, and she always won, So I made her give me a head start.
Alas, it was to no avail. I wasn't halfway to the finish line that we had drawn on the pavement with a chunk of brick, before she passed me. Not too many seconds later, as we approached the finish, Joy's foot slipped off of the pedal of her bike and she drove her big toe straight into the pavement. Of course, it not only hit the road hard enough to split the nail, but the toe drug along on the abrasive surface for quite a way before Joy's bike came to a halt.
She was screaming, I was crying and Joy's toe looked like it had been through a meat grinder. It still makes my sphincter tighten a little, just to think of it.
So, enjoy your SPD pedals, and Keens, and whatever other open shoe you want to ride in. I'm sure the wind between your toes feels quite nice. As for me: Gimme shoes, every time!