I agree with the other posters, and let me just add:
Monsanto sells a wide variety of corn seed hybrids, many of which are GMO, and some of which are not. They are also not the only seed company out there, although they have the largest market share.
There's no proof that any of the many varieties of GMO corn out there (sold my Monsanto or others) are carcinogenic. All GMO is, is an advanced breeding technique to create new hybrid varieties of crops. There's nothing inherent in the technique that would cause the offspring to be harmful. However, that hasn't stopped a large number of media outlets from criticizing GMO crops as "unsafe" or at least calling their safety into question. And to be fair to their point, there also are not a lot of long-term double-blind studies out there showing definitive safety on the part of GM crop varieties. If you haven't seen media criticism of Monsanto or GMO crops you've had your head in the sand. They're very controversial (at least in some circles).
To answer some of your other questions: what percentage of Americans consume it (GMO corn)? Probably 90% (for many years now) via a few avenues. Most grain corn is used as animal feed, and the meat from those animals are then consumed by people. Corn is also a direct ingredient in a lot of food (corn chips, corn flakes, corn muffins), and finally people consume it via corn syrup sweeteners. You'd be seeing a lot of dramatic adverse reactions among farm animals and people if GMO corn were carcinogenic or toxic in some way, and that hasn't been the case.
Why not reform the FDA? Well the FDA makes its decisions based on science, not rumor or speculation. The FDA as far as food safety goes, is focused on eliminating biological contamination from the food system; things like listeria, E. coli, salmonella, and other contaminants that we know are toxic and that do cause illness and death every year. They're in the process of implementing the Food Safety Modernization Act to address that issue.
The bottom line, however, is that you don't have to eat GMO crops if you don't want to. A big part of the organic farming movement is avoiding GMO technology. If you don't want GMOs you can buy organic and avoid them. There are also some third-party certification companies out there that are certifying foods as GMO-free if you don't care about the rest of the organic standards.