What are the positive and negative effects of introducing a gene for herbicide resistance into a crop?

The positive side it cuts cost for farmers.  On the negative side it encourages herbicide use which is not good for consumers.  Also plants share genes and some related weed will pick up the genes for herbicide resistance and then it will be very hard to kill.  Then you will have to use even stronger herbicide to kill these weeds.  Which in turn puts more herbicide poisons into the environment.    Making plants herbicide resistant is a very bad idea

John h  I am always open to new ideas.  Could you explain to me why less herbicides are needed with herbicide resistant crops.   Also if there is only a one time transfer of the resistant gene to a weed, why is that not bad?  After all one weed can become millions.  Also do you work for the companies that make these products.  Because in my experience company employees are not always a good source of objective information.

Corn is a grass.  Corn fields are surrounded by grass type weeds.  If the herbicide gene gets transferred to just one of these weeds than that weed has an advantage over all the other weeds that are in the cornfield.  When the farmer sprays the weeds this resistant weed will survive and become more plentiful.  Eventually most of the weeds in the corn field will be resistant to herbicides.   Then the farmer will be forced to use even stronger herbicides to kill these herbicide resistant weeds making the corn more contaminated with stronger herbicides.  The benefits of herbicide resistant  corn is short term.  In the long run we all lose.

The positive side is many.  It cuts costs, increases yields, provides a much cleaner product for market.  Contrary to popular belief it greatly reduces the use of herbicides.  The chances of it spreading to other crops and weeds has been shown to be near zero. The negative side has been very little.  One is it tends to encourage the wide spread use of single genotypes which can diminish genetic diversity in the crop.  If you had asked about GM crops for insect control there are a few more disadvantages such as beneficial insects that could be killed along with the one it's aimed at.  The main disadvantage of GM crops is misinformation to the public and suspicion because people don't understand GM crops.  I realise that this is probably not the popular answer that you are looking for but as a scientist it is my opinion.