GMO cultivars usually do not contain new, man-made chemical compounds.
For example, Golden Rice contain beta carotene (occurs naturally in e.g. carrots).
The virus resistant Hawaiian Rainbow Papaya contains a protein from the virus' capsid, effective "vaccinating" the plants, resulting in virus resistance.
Bt Cotton contains a chemical from Bacillus thuringiensis, a common bacterium in soils, that is harmful to pest insects.
New, man-made chemicals aren't intrinsically bad. But based on past experience, we are right to be cautious because we can't always anticipate their effects, the effects can take a long time to become apparent and they can be impossible to eliminate (like with PCBs).
But you can't. For example, organic farming uses much more pesticide and herbicide than the same GMO crops do. There is a persistent myth that organic doesn't use herbicides and pesticides but it is not in any way true and never has been. But +1 to the marketing department for implanting that persistent idea in the mind of the general public.