Its not that bad, many worse things you can eat. The reason why people say white rice is bad is that it can be considered a "processed," or "refined" food.
The processing is that the natural bran component of the rice grain has been removed. This eliminates the natural fiber, various Vitamin Bs, and other nutrients that are good for you. The white rice folks will then spray vitamins and minerals back on the rice to try to put back the nutrition they removed in the first place.
They still miss some things, and the most glaring omission is the fiber.
Why take off the bran and attempt to make up for it with artificial vitamin addatives? Because the fiber contained in the bran coating on natural brown rice makes the texture slightly more chewey, and it also makes it take twice as long to cook, both considered negatives by the vast majority of rice consumers.
When you eat white rice, since the fiber for the most part removed, your system digests the grain very rapidly, breaking the rice starches down into glucose (sugar) much more rapidly than if you ate brown rice (the bran coating of fibers slows digestion down significantly).
Essentially, what you get with white rice is an influx of sugar in your bloodstream that is not mitigated by the natural slowing action of the bran fiber. This is why some consider white rice not terribly healthy.