God is omniscient. This is a defining characteristic of most gods. For the purposes of this argument, I'm dealing with those gods.
My uncle is a dentist. About once a year, he performs a procedure on a blowfish. A local restaurant owner has a pet blowfish that he considers the mascot for the restaurant. A blowfish's fangs grow over time, as they trim them down by chewing on coral. This blowfish, however, has nothing on which to chew. Thus, he nearly starved to death because his fangs grew so large that he couldn't fit food into his mouth. My uncle saved his life by becoming the first dentist to perform this procedure. And now he does it yearly, because the fangs keep growing back. It's difficult (for everyone) and dangerous (for the fish).
This is evolution in action. It's short-sighted. Evolution sees (figuratively) a niche, or a problem, or a weakness, and it latches onto the first solution that comes along. That solution works fine under the current circumstances, but evolution doesn't know enough to plan for the future. It doesn't consider that circumstances change. It just react to current circumstances. If those circumstances last long enough, you get some really weird stuff. If they change, species go extinct.
We can see examples of short-sighted biological developments all over the world. Moths fly into flames because they use light from the moon and stars to navigate. They didn't expect that we might find a way to have light while it's dark, and they certainly didn't expect that light would kill them. Fortunately (or not), there are plenty of moths and their population can withstand the fairly modest number of candle-related casualties they now suffer.
Being prone to addiction is a biological condition. Some have suggested that it might even be a desirable trait on some levels, as addicts have proven time and again to be extremely resilient when it comes to survival (as far as natural selection is concerned anyway - it doesn't care if you live to 80, just as long as you have babies before you go). Striving to satisfy that craving provides motivation to a creature, whatever that craving is. That creature will go to almost any lengths to get what it wants, and that resolution helps them survive until they get it. The consequences of addiction are largely unimportant to evolution. Lost your job? Died at 30? Got thrown in jail? Killed someone? As long as you had kids, and there's a good chance you did, natural selection is happy with its choice.
Flawed biology simply doesn't make sense for an omniscient god. Why would you build things with such remarkably crippling flaws when you can clearly see the problems that will arise? How can an omniscient being be so short-sighted? Why build things with a predisposition to suffer and fail?
Nature has an obvious bottom-up design. It is complicated, convoluted, and confusing- a complete clusterfuck. The course of its progression makes your average MMORPG's design look positively prescient. (Boom! Take that, MMORPGs!) It is short-sighted and flawed, but beautifully so. It could not more clearly resemble the rule of chaos- undirected and free. It lacks intent or direction, or any other stain that would have been left by a thoughtful creator.