There are many places where new highways/freeways are needed, and many places where expanding on existing roads makes more sense. To say that because YOU live in a place where there is no need for a new highway that it isn't a good idea to build new ones just shows the limitations in understanding that so many people have.
One thing that adds to costs of goods is the cost of shipping. If you have a very rural area that has small roads with only one lane in each direction, that means that transportation of goods will slow down, and that increases costs. The whole Interstate system in the USA was introduced to help deal with that issue, but there are still MANY places that have a horrible road system. There are also areas where you can NOT widen the existing highways due to limited space, or where it would help, but not do enough in the long run.
On the flip side, many people do not know what it is like to live in a small town in the middle of nowhere, and where you need to drive 30-45 minutes just to get to the nearest highway. If you did, then the idea that a new highway that connected your town to the rest of the world would be a really big positive, and would open the doors for more businesses to move into the area, which means more jobs. Adding highways to an area that already has one or more highways just does not sound like it would help, though it CAN.
The big thing is that people should not assume that their own personal experiences apply to EVERYWHERE. People in the Northeast USA really have very little comprehension of what life would be like in a small town in Kentucky for example, because it is going to be VERY different. Then again, most people have a problem with thinking outside the box, or assuming that knowledge of EVERYTHING around you will prepare you for anything that might happen. Isaac Asimov understood this very well, and reading the Foundation series(both the original trilogy as well as following books) will illustrate that idea. The more you think you understand everything, the less prepared you are for the unexpected.