There are plenty of people in the world, whether they be Christian or not, who, while describing the various attributes of their god, describe their god as being "perfect". They say things such as this, from Omegafaith:
God is perfect in grace, in wisdom, in knowledge, in beauty, in holiness, in love, in power, in righteousness, in justice, in all that He is and all that He does. There is no thought or word or deed of God that is less than the ultimate it could be.
It is not that God does things perfectly, it is that He Himself is perfect and, therefore, all that He says or does is perfect. God cannot issue forth from Himself anything that is imperfect, for imperfection does not dwell within Him. Not even the possibility of imperfection can be found within His being. We creatures of God, products of the Adamic fall, should take great joy and hope in the perfection of Him who created us.
Perfect, in this sense, means without flaws. Perfect also seems to mean incapable of being flawed, or eternally perfect - perfection is an attribute of their god that does not change. It is impossible for their god to be imperfect. I would venture to say that all people I know who claim their god is perfect, also claims that their god's perfection is eternal. In this eternal perfection, it does not matter what their god does or how heinous their god's actions appear to be, that god is still perfect. Every action he does is justifiable by his perfection.
This disgusts me. Unless you subscribe to some sort of notion that everything in life is perfect, people generally don't ascribe eternal perfection to anything else in our lives. If my otherwise awesome and perfect-for-me boyfriend were to get angry and punch me in the face, I would immediately question his perfection. I base my attribute of perfection on actual observation, experimentation, and rational analysis of perceived flawlessness, rather than insisting that my boyfriend is still perfect, and that his action of punching me in the face was totally justified given that he is perfect and thus incapable of making a mistake. Nothing else enjoys the you're-always-right card, so why does someone's god?
Perfect, to me, does not mean "incapable of being flawed". It means that the entity currently being described as perfect currently has the property of perfection. As an example, I might be able to create a perfect scale model replica of a 1977 Corvette Stingray, but if said model falls off my mantle and breaks into 35 pieces, it is no longer perfect. It was, but now it's not.
The problem is not only one of irrationality. If one insists' one's god is perfect, then one can rationalize all sorts of terrible, unjust, immoral, hateful things because one can rationalize that anything at all god does is perfect because that god possesses the quality of eternal perfection.
I think that some Christians take it as fact that their God is perfect - and based on that perceived fact, they rationalize all of the immoral, unethical things in the Bible as part of their god's perfect plan. In this way, the seemingly terrible actions committed by their god must be perfect, because god is incapable of committing imperfect acts.
Atheists on the other hand do not take God's perfection, must less his existence, as fact. We see the killing and vengeance in the Bible as terrible things, not necessary acts perpetuated by a perfect god. Instead of rationalizing those terrible things as perfect things, we judge this god by his actions. It makes far more sense to determine a given god's level of perfection based on the actions of that god.
The problem, as usual, lies not so much in the logic but in the premise. To propose that god is perfect and to then justify all of his actions by claiming those actions are perfect is to put the cart before the horse. Instead, we should look at individual actions that god supposedly perpetrated and ask ourselves - would a perfect entity do this? If there is a better way of accomplishing whatever it was that god was trying to accomplish, then the answer is clearly: no.
Nothing deserves to have the attribute of eternal perfection in our daily lives, so why should someone's god? That god should be held up to the same standard of observation and rationality as everything else in our lives. People don't ascribe other people's god the attribute of eternal perfection. They look at Zeus or the Muslim version of god or whatever god they don't believe in, and they can see clearly why this god is not perfect, but they fail to see the same flaws on their god.
If you believe your god is perfect, what would that god have to do to make you change your mind? If your answer is, "Nothing." then I question your ability to think rationally and make intelligent decisions for yourself. I question your morality, as your perfect god could do anything, anything at all, and in your eyes he would still be perfect. I question your ethics and your judgment. Whatever happened to falsifiable hypotheses?
There are three ways (there are possibly more, but two for the sake of this argument) to decide that something is perfect:
1. Look at any given entity X and observe it's characteristics and determine the status of its perfection based on those observed characteristics. In this case, perfection is determined based on experience I.E. a given entity is perfect because we have observed perfection/lack of flaws/completeness.
2. Define a given entity X as perfect, in which case no observable characteristics will change its status as a perfect thing. In this case, a given entity is perfect in spite of any flaws one might encounter - those flaws are dismissed as not actually being flaws, because the given entity has already been defined as perfect. This is using an a priori definition and is independent of experience, I.E. A given entity is perfect because it is perfect.
3. Define a given entity X as perfect, and then if any attribute Y of X is determined to be imperfect, insist that the individuals attributing Y to X are mistaken.
The first way of deciding that something is perfect fits in with our observational model of the world - observe, experiment, and think about what has been observed and experimented on. The second and third way has nothing to do with our observed world. The first way is rational, and the second two are not.
Imagine, if you will, that I think my boyfriend is perfect. If I think he is perfect based on my observation and experience - if he's awesome, intelligent, sexy, thoughtful, etc - then his perfection is subject to change say, if he decides to kill my cats because I looked at another man.
If I think he is perfect because he is perfect, then his actions do not matter, as his perfection is not based on my observation and experience and not subject to change. He can kill my cats because I looked at another man, and his actions are still perfect - he did the right thing. I am the one to blame.
If I think he is incapable of being imperfect, I will deny that he killed my cats.
This type of reasoning is, frankly, dangerous.