Biologically, a world without disease and pain and such just isn't really possible for reasons which would take me hours and dozens of posts to try to get all of my thoughts across.
Well, if God has the power to heal, but does so on his own whims, then a world without disease and pain is possible. No? It would also mean biology and other sciences are a lie, since God can alter them how he pleases.
This is why I brought up the whole God, tyrant and control over one's life issue. If God has this power and delivers it whenever he feels like it, it's similar to a tyrant. In conjunction, it means we have no control over our lives and are just puppets.
If God had the ability to do so and has been doing so, we'd have evidence. (Wow, this is why I hate debating this.) And right now we have a pretty darn good understanding of how the universe works. Until we see something to the contrary, I have no reason to debate this.
For a world without, say, bacterial disease, all bacteria that are harmful or potentially harmful to humans would have to be eradicated. In addition, all bacteria that could potentially mutate to become harmful to humans (which isn't hard because bacteria can mutate very quickly and can even transfer DNA between each other, altering their genomes) would have to be wiped out, or altered so that they could not affect humans. Literally every single bacterial cell on earth. When you affect all of these bacteria or kill them, you're altering the global ecosystem in an almost incomprehensible way, since bacteria make up such a large percentage of all life on earth. The result would be mass extinctions. This is just one tiny example. For God to bring a world without pain or disease would mean to completely shatter everything that we know about the universe from thousands of years of scientific study. If you choose to believe that God is a puppet who controls everything on earth, just know that every single piece of scientific work in human history contradicts that.