what poisons enter your body

 if the laws dont force companies to label their products to have GMO, why dont companies which do not use GMO advertise themselves to have no GMO.

People who care will go for the non-GMO products. Companies who don't use GMO would benefit from this advertising and increase their profits, they can even charge higher prices just like organic food costs more than regular food. 
If due to monetary incentives, the politicians and law doesnt protect society by letting you know what enters your body, then market forces that bring forth cheap but gmo food,could also create a market for more expensive but non-gmo food. 

But perhaps it is too late, and most producers use stuff which you wouldnt want in your body, like msg, gmo etc. Perhaps such producers became the monopoly power.