In a perfect world everyone driving on a freeway would know HOW to drive on a freeway. Simple things like getting on and off safely. But that is just not always the case.
Those who insist it is easily avoidable with a little defensive driving are not being realistic. When you are in the right lane and choose to slow down every time you see a car on the ramp, all of the vehicles behind you also have to slow down. If you choose to speed up, how long before you are dangerously close to the vehicle in front of you? If you choose to move into the left lane, where vehicles are often moving faster, you have to accelerate with your trailer into that lane or hope the vehicles in that lane are all ready to slow down for you. Any one of these actions can have a ripple effect that is possibly dangerous. We haven't even talked about snow, ice, rain, impaired drivers, etc. In light traffic it won't be much of an issue, but many of us drive where roads are heavily traveled.
I'd rather see one driver who brought it on himself skid to a stop than multiple drivers have to all skid to a stop on a freeway.
Sometimes defensive driving means holding your course and speed.