Well, some people can descend pretty safely at high speeds. I am really not comfortable going much over 40 mph on a descent. Like you, I think of the consequences of falling at high speed. Generally, if you are not comfortable doing something, it probably is not a good idea doing it. Going beyond your comfort space makes one more prone to accidents. Now many people can descend at very high speeds safely (over 50 mph). But it never appealed to me. This is supposed to be fun.