It's funny when it comes to scooters. They are perhaps the most common vehicle one sees in cities of Europe, and they are respected by the other traffic.
I rented a car on St. Croix once and almost got in a wreck. I was doing fine driving on the left until I got to an intersection where I needed to turn left. Habit intrusion caused me to select the right lane when I turned onto the new street and I almost hit a truck head-on.
I supposed it would be different if I was staying on an island for a week. I still wouldn't rent a scooter but probably would get a car - and be especially careful while driving it. But for a cruise and the few hours one is in a port, it just doesn't make a lot of sense to rent anything.