Whether the pros outweigh the cons of pesticides is dependent on which pesticides you consider and who is affected by pesticides.

It’s important to realize that pesticides are used nearly everywhere for farming. A pesticide is basically any substance that kills something that’s going to harm your crop, whether a plant, bug, fungus, or bacterium. Even organic farming uses pesticides, but doesn’t use what they consider to be “synthetic pesticides.” If we don’t protect crops in some manner, a large percentage of the crops will die before we can eat them. We’re competing with a lot of different organisms for the nutrition of the crops. If everyone stopped using any substance that could be considered a pesticide, it would be catastrophic and probably billions of people would starve to death.

When the Earth had only hundreds of millions of people on it, pesticides probably weren’t as necessary. But now that the population is 7 billion, pesticides are crucial for maintaining and increasing that number. That being said, certainly there can be negative effects of pesticides. Some are harmful to humans, though it’s only a problem for the people spraying the pesticides rather than the consumers of the crop.

In developing countries where farm workers don’t have much protection when spraying pesticides, there is an increased risk for illness. Though either way, by time the product gets to the consumer, there is not a biologically relevant amount of pesticide left in the product. And killing of organisms that aren’t supposed to be targeted by the pesticide is also problematic.

Now looking specifically at the problem of bee death, or colony collapse disorder (CCD), pesticides are probably a significant factor. However, they are almost certainly not the only contributing factor. Many pesticides do appear to have a stronger effect on some bugs than others. In the case of bees, a particular family of pesticides called neonicotinoid seems to be involved. The current perspective is that the pesticides don’t kill the bees, they stress them. A stressed bee may not be able to deal with a parasite, virus, or conditions due to climate change as well . Therefore, there are many factors interacting with each other in a complicated manner that has caused CCD. If only pesticides were eliminated, it is entirely possible that the problem would persist, perhaps with less intensity.

1. That's a complicated economics question and really not one that can be answered scientifically. However, pesticides generally are only a temporary solution to insect pests, because the insects subjected to pesticides will eventually evolve resistance to said pesticides. This will force us to either use new pesticides, come up with some other form of pest-control, or just accept living with the pests.

2. Yes, and work on this is being done. Among the most favorite are something called biocontrol agents: other living things that we can use against insect pests like biological weapons, and which can either evolve naturally (some wasps) or be engineered (some bacteria) to be only deadly to specific insects, namely the ones that are acting as pests. The pests will eventually evolve resistance to these controls, too, but creating and deploying a new biocontrol agent is less environmentally destructive than a new generally toxic pesticide.

3. Good question - the answer is sometimes yes and sometimes no. You're probably familiar with the idea of swarms of locusts (grasshoppers) from the Old Testament and other places, which indicate that yes, sometimes pests really can cause famines and other catastrophic devastation. The amount of organic produce that you can buy in stores, however, tells you about what pest damage looks like more often: not having pesticides or genetically-modified produce means that the produce is less plentiful and so more expensive, but there are still farmers who do well enough to make a living off of it.

One more thing that you aren't considering: bees have their own pests, among them a mite that infects bee colonies and kills the bees inside of the colony. There is good evidence that the die off rates of honeybees are due to this mite as much as to pesticides.