Confirming the safety of GM crops is simply infeasible. It is certainly possible to carry extensive studies in a limited number of GMOs and conclude that they are reasonably safe, but the very nature of genetic modification - and its value, therefore - is that its potential is by all means boundless. One can modify a crop to produce substances that are poisonous to humans just as easily as they modify a crop to produce substances that are toxic to weeds or insects, thus rendering it more "resistant".
The very nature of the concerns about GMOs is that it is very difficult to identify and measure the metabolic side effects that originate from modifying a single gene or group of genes. It's crucial to keep in mind that scientists are *constantly* identifying previously unknown compounds present in even the most common of the vegetable species. It is nonsense to think that it would be possible to measure all the metabolic alterations arising from modifying, adding or deleting a gene.
On top of that, there is an intrinsic issue of conflict of interest. The entities who are most qualified to understand the holistic effects of a genetic alteration, namely the companies who developed the GMO, have no incentive to invest in extensive analysis that may result in findings that render their new product worthless. Pharmaceutical companies are forced to do just that for new drugs, but the food industry is not nearly as regulated and probably never will be.
Given the enormous potential for unknown (and unnoticeable in the short term) side effects of consuming GMOs, I personally refrain from getting close to them at least until I have any trust that proper procedures are in place to thoroughly evaluate them.