First off, talking about the nature of man using the words "good" and "evil" shows a lack of understanding of the subject matter. While I VERY GENERALLY agree with what you're saying, I feel that some clarification is in order.
Define "evil" here? Rape? Murder? Define those acts? Simply having a shitty attitude is not "evil". Not helping out someone who is drowning is not "evil"... apathetic or cowardly to a criminally negligent extent... sure... but EVIL? Hardly.
The nature of man is self service. Man wants first and foremost what is best for him. By nature man wants multiple sexual partners, anything he sees that he wants, etc etc. It is social constructs such as monogamous relationships and property laws, along with their consequences that make him not follow these urges.
People in the US and most "civilized" cultures would say that cannibalism is evil... but we know that it has been done by "civilized" people in extreme conditions... shipwreck victims adrift at sea... frontiersmen lost in the mountains... plane crash victims in remote areas...
Were these people evil? No. They were following the laws of nature and survival.
Nature is not a friendly place. It is survival of the fittest. Animals kill and eat other animals to survive... they aren't evil for this... they are simply surviving... and as you would probably put it... following the obvious will of god for creating them that way.
We really do have free will... and just because some people truly have no conscience in the sense that they don't respect the lives or property of others... this doesn't make them EVIL... the idea of EVIL is a concept created as part of religious fairytales... black and white... good and evil... and to start categorizing the real world in such a binary manner is simply WRONG.
I do feel that man is by nature selfish... and that that selfish nature is destructive to the world we live in. Generally given the option to serve ones self without the possibility of serious repurcussions, man would do so most of the time... mind you, not all of the time... but most.
This is what has led to things such as law and religion... to setup consequences... both in the material and the spiritual realm... a sort of double fisted approach to reign in the consciousness of the people. If you do something wrong, either you're going to get caught, and get put in jail, killed, have your hands cut off... etc... or even if you don't get caught... there's always the religious approach that states that you're still going to pay for it. God will get you and you'll go to hell etc.
It's easier to just say that people are evil than to understand that we are just animals... capable of free thought and capable of every deed that you can find anywhere throughout the animal kingdom. Just because we've evolved this much, doesn't mean we don't still have a lot of those animal aspects still. We are still predators... forward facing eyes... canines and molars for both ripping and tearing meat etc... and for eating vegetables and such as the omnivores we are.
Man has labeled certain actions "evil" to give them a social stigma... because they are unpleasant and/or undesirable (to say the least in some cases). But in the end, that label is just an arbitrary construct created by man.
Given that in the end there is no such thing as good or evil in some spiritual battle over the fate of mankind, but simply us as humans, with free will... doing what animals have done since the beginning of life on earth... live and breed... by whatever means necessary... your imaginary god simply doesn't figure into the real world happenings. It's nothing more than nature... the way it was long before mankind... and if we are too stupid to avoid our own destruction through nuclear war... or simply from a meteor wiping out around 84% of life on earth AGAIN... (yes, there have been several mass extinctions on earth, and the one where the dinosaurs died was not the worst)... life will go on as it has in the past.
I should probably put together a list of reading material to familiarize you with some of the topics that would give a better insight into the concepts above. I know that some of this is culled from my Cultural Anthropology studies in college... but mostly from a wide variety of sources.
that one covers a lot of the concepts I've tried to convey here in greater depth etc.
Let's boil it right on down. Man is just another animal. An animals primary biological function is to survive and breed. Looking out for the best interests of others is of secondary importance. While it is "admirable" for people to do such, it is only perceived as such because man has labeled it so. This is simply an extension of organisms living in groups giving up some amount of freedom in order to gain the safety of numbers found in a group. In such a group, it is undesirable for one of it's members to disregard the well being of the group in some manner for it's own benefit. Any such action, while possibly bad for the group in part or as a whole, is not evil... but simply the way of nature and unfortunate for the weaker party on the receiving end.
That's life. Survival of the fittest.
Sorry dear, real life isn't a fairytale and there's no man in the clouds to make it all better.