As someone who races time trials at least weekly, I have raced various types of course. SC, DC, SPOCO, Hill Climb and my personal opinion is that racing on DC's (the ones I have raced on anyway) is a reasonable thing to do. I think of it in risk assessment terms, frequency of incidents is lower on DC's, severity is higher. On SC and SPOCO courses, incidence rate higher, severity lower, in risk assessment terms, the risk is around equal. I deem the chance of incident on a DC course low enough for me to ride it (course and condition dependant, I have DNS'd twice this year on the A50, due to excess spray and reduced visibility - both events did go ahead and many people did ride, without incident), some people think otherwise, thus they are welcome not to ride. Of course this will mean certain events end up missing some strong riders, but then again, every course will put some of the big names off.
I mostly race local on SC courses and I enjoy it, but I am not opposed to and will travel to fast courses a few times per year.
I've raced on various DC courses, including the A50 between Blythe Bridge and Uttoxeter and the A63 at South Cave.
The reason I go to these courses is ultimately for the fast times, but also because they attract riders from all over the country so you get to test yourself against fast men from all over the place. On top of that, it is a different kind of race and it offers a change of scenery, you can see ahead a long way, the surfaces are usually pretty good, cars can see you from a long way back (especially if you have a good rear light, which is something I do have), there are no real technical elements to contend with etc. In a way it is a dumbing down of the race, in a way which lets you concentrate on other things more carefully and experience the act of racing in a different way.
Subjectively speaking, I feel a lot more on edge racing SPOCO events than riding down a DC (which doesn't put me on edge at all)! Certain things happen with such frequency on my local SC courses that I now pre-emptively try to control the road at certain points in anticipation of the silly manoeuvres! On DC courses I don't recall a singe incident to date.
Roads are not dangerous , impatient nobs in cars are though , only reason they TT on these roads is for a quick time .
That's part of it, but not the only reason.