There is a huge difference between naturally crossing plant genes through selection and breeding and gene splicing. Frankly, I'm sick of hearing this "we've been doing genetic engineering through agriculture for decades, this is no different" bullshit. Whether you like it or not, there is a huge difference between crossing genes that have long (I formerly said "always" here but that's a bit extreme considering evolution) been present in a particular species the "natural" way and injecting foreign genes the artificial way.
When breeding plants through crossing, you are dealing with a gene pool, that, through millions of years of natural selection, has been selected to work for that particular species. There is always a slight risk of genetic defect during reproduction, but for the most part, we are dealing with genes that "nature intended" to be there.
When one artificially splices DNA, we are dealing with genes that were never there to begin with. What's the difference? WE DON'T KNOW EVERYTHING THERE IS TO KNOW ABOUT GENES! In fact, the very definition of a "gene" is still something that we debate today. There is a world of difference between looking at the finished product and saying "this plant must have good genes, let's make sure we use them again," and specifically picking out certain chunks of DNA from one species and plopping them into another. Let me say it again; there is a WORLD OF DIFFERENCE. Sexual reproduction is natural, and involves genes that are known to work correctly for their purpose.
Did you know that, depending on where you begin decoding, a single "gene" can represent more than one protein? DNA is not as simple as we think it is. In many cases it is redundant, in others, it seems compressed. We don't know all there is to know about DNA, despite the fact that we know how to make copies of it. This is the problem with gene splicing. We could be inserting a gene that codes for a certain antibody in one species, yet is completely worthless in another, depending on where it's spliced in. We could insert a gene that not only does what it's supposed to do, but something else that we never intended. Genes code for proteins. Many lethal poisons are proteins. Many proteins provoke allergic reactions. So if we're coding for proteins we aren't even aware of, there is plenty of room for negative side effects, like food allergies we didn't even know existed (until we created them).
When you breed plants, you're taking a gene pool that has been suitable FOR THAT SPECIES for millenia. Adding genes from an external source is in no way the same thing.
And if it's a death sentence to label food as "genetically modified," then so be it. If the public is afraid, educate them...but at least let them know what they're eating. The biggest problem with this genetically modified food bullshit is that genetically modified pollen can easily spread and reproduce with non-modified plants, making it nearly impossible for anyone to claim "not genetically modified." Doesn't anybody remember the precautionary principle, for cryin' out loud? I think mother nature has given us some good genes to work with, and I'm sick and tired of companies like Monsanto trying to solve the very problems they've created by creating new potential problems...for example, "RoundUp Ready" soybeans.
EE: Even though Everything is not a BBS, I will take a moment to respond. What you are basically saying is that, because retroviruses are known to randomly move genes around (between different species) with little apparent consequence, deliberate attempts by humans to most intentionally create consequences won't pose any more significant of a risk. While retroviruses may indeed be facilitating inter-species sex on a regular basis, that is no justification for us to do the same, mass produce it, and base our very existence on it. I'm not saying that every set of genes is written in stone and will never change, but human efforts to make intentional changes must be done so with caution, since the changes can easily manifest themselves in the wild, and can spread throughout a species without our consent or control.