I was running a 44 tooth chainring on a 16 tooth cog: 74 gear inches. I can easily cruise in that, but coming off of the many red lights in Tokyo, and a hill at the end of twenty kilometers, it was a little higher than I wanted. I switched the chainring for a 42 tooth, which though only 5% easier has made those two things much easier. I do find myself getting spun-out sometimes, but that's the price you pay. Suppose it is good for my souplesse. Fact is I just needed to use that headline for a post.
Here's the best reason to ride fixed: never look away from traffic. The real reason I have not had an accident yet ('knock on wood') is that I do not look down to shift, especially when I have no other gears, do not look down to clip into my pedals, and do not look at a map/GPS while moving, or when getting my water bottle. These and a decent sense of propinquity. Look ahead and shoulder check, and assume nobody's looking for you.