The most commonly cited argument is the increase in traffic fatalities, which despite the Daily's desire, has been well documented to increase with higher speeds. The second most obvious cost, also thoroughly documented, is a decrease in fuel efficiency. There are other costs associated with increasing the speed limit that are less obvious, but real nonetheless. First, there will be a great deal of tax money spent to manufacture and install signs for the new speed limit.
Faster speeds result in deadlier and more destructive accidents.
Psychological costs should not be discounted. Twenty years ago I knew that the speed limit was never more than 55 mph, and if I traveled to another state of the union, this was a fact on which I could rely. Giving states the freedom to set speed limits has resulted in confusion for all of us. Undoubtedly there are other costs. I say no, and voice my opinion by driving 55.