1. If we continue our use of herbicides/pesticides to the point of wide-spread colony collapse, spread of plant disease (perhaps canola, soy, or corn), significant reduction of nitrate fixation, increased human cancers we may also see hundreds of millions of people die or be without food.
Obviously, no one is suggesting we stop producing enough food for people to eat. But you need to look past the next 5, 10, 25 years. Those issues listed above are all real. And can all be linked to herbicides/pesticides and monocultures. We need to work on a new solution, a new system. The current situation is not a long-term answer.
2. This is more a theoretical morality issue. How much control/ownership should any one entity be allowed to have on life. What if they aren't just patenting seeds for RoundUp resistance? More so, say I live in a certain climate where I want a certain field tomato to grow. And under those circumstances I end up with a seed similar to a patented Monsanto seed. I lose in court. Other varieties of tomatoes don't grow will in my area. What do I do? I no longer have the freedom or right to grow successful tomatoes. This is not reality, but a possibility. One, that I do not believe in the slightest is worth risking. This could also lead to outrageous seed pricing.
Oh while I'm at it. Let's add climate change, land degradation (http://news.mongabay.com/2006/1214-unu.html). Basically, yes we need to feed billions, but we also need to do that 25-50 years from now. The practices used for high-yield crops are limiting our ability to produce food in the future.