There is much confusion about the difference between Hybrid vegetable varieties and GMO or "Genetically Modified" varieties. Although many tomato plants are "Hybrid" varieties, which means they are cross bred by a "Mother" tomato and a "Father" tomato (by the birds and bees method). This is to assure that the best traits of each are preserved, and does not mean they are GMO and they are completely safe to grow and eat.
Genetically modified seeds of soybeans and corn are currently grown and were developed by altering the actual DNA of the plant and producing seeds from that plant. This is done in special laboratories to change the plant characteristics to resist diseases or insects hoping to reduce our dependance on pesticides. This modification was marketed primarily to large commercial farms wanting to use less toxic materials to kill pests such as corn ear worms.
Although this is a commendable venture, we aren't sure this is the best way to go about it. Also, if a food source for a particular insect is eliminated, and therefore that insect population starves to death, the next one on the food chain may starve and on up, or on down, until our environment is detrimentally affected by the loss of a species, which may be as simple as a common bacteria, necessary for our survival. Also, "Roundup Ready" soybeans actually allow for more herbicide spraying, not less, which completely negates the argument for GMO's.
If you take the approach to gardening to only kill what is absolutely necessary to prevent serious damage in the garden using the least toxic method to other species of insects and fish you are growing organically and that means avoiding GMO's. Keeping bees and fish healthy and happy keeps us healthy too. Although it is unlikely that genetic modifications would affect the eater of the product, the environmental effects are still very uncertain at this time. At http://tastefulgarden.com we have signed the Safe Seed Pledge and all of our vegetable plants are non GMO, and will be as long as we are in business.