1. The more skilled a craftsman is, the less defects his product contains. 
2. The perfect craftsman is an omnipotent creator (a.k.a. "God").
3. God should therefore be capable of producing a creation without any sloppy defects.  This includes humans, of course.
4. At the organ level, the inflamed human appendix is an obvious defect of design.
5. Ergo, humans are far from being physically flawless. In behavioural aspects, Christianity largely agrees. 
6. One is compelled to conclude that one of two possibilities is true: (1) "God" is not omnipotent (and therefore is not a god), or more likely, (2) "God" does not exist.
Q: God's "cosmic plan" is perfect, and this does not require that its agents be perfect. In other words, God could have deliberately made us flawed.
A: The perfect plan is the most efficient, or one that takes all possible shortcuts. Christianity makes the assumption that God's plan is to "save" his "children" from our sins ("defects"). Well, why waste resources and sweat with all the protracted "saving" if the universe could have instantly been made perfect to being with? Then God wouldn't have to bother with hell. Unless God wants us to suffer, which doesn't seem to be evidence for an all-merciful deity.
 This isn't meant to be sexist but to remain in line with the fact that most religions are patriarchal.
 "Defects" are defined as superfluous aspects of a design that do not make any positive contributions, while being potentially harmful to the proper functioning of the creation.
 It's odd that Christianity teaches that humans are fundamentally flawed. Obviously, its adherents don't trust God's ability to debug his programs. Jebus was an equally ineffective software patch, since exceptions (sins) are still being committed by Christians.