You may be correct when it comes to your last statement. However, Budhdha said that there is karma and you should do good karma. Anyways, one can be good based on karmic believes and also one can be good based on some doctrine other than karma, say ten commandments for example.
Anyways, so you are telling me that you are doing good, and by doing so, you are hoping to be a decent human being. But why? Whats the point of being a decent human being? Consider what happens when go to a dentist (like dath kimbula). He would use his variuos devices to drill your teeth, and to do so, he would numb your mouth by some sort of injection. Plus, you need to pay him too. (Well, if it is our dath kimbula, he would not take money from you. But, a typical dentist would ask you to pay) The point is, if going to the dentist does not give you a benefit, namely good oral health, there is no point of going to the dentist and getting your teeth drilled. It would be a waste of money.
Being a decent human being is also like that. It is not a easy thing to be decent. Being decent has a cost, just like going to the dentist. Donating for charity is a good thing, but doing so eliminate your chance of spending your money for something that serve your interest. So, after all, why be good and decent by undergoing the cost of being decent. Whats the point? Well, being decent has social rewards. It saves you from going to jail. So, is being decent something like going to the dentist? In other words, is the only reason for being a decent human being is the fact that the consequences of doing so (avoiding jail sentences) is desirable?
Since you do not believe in karma, are you being decent only for its desirable consequences like avoiding jail sentences? If not, why are you being a decent human being? Whats the point?
If you are being decent to avoid being arrested, it entails that you only need to appear as if you are a decent human. Do you still think you should really be decent, or do you think that all you need is to simply appear as decent.
If you think that you shoul really be decent, then why?