Human-Chimp Similarities — Why?

Proselytizers of microbes-to-monkey evolution are known to point out that humans and chimpanzees have some things in common, even citing spurious data about genetic similarities. EDIT: The preceding link is now out of date and in dispute. See "A Fresh Look at Human-Chimp DNA Similarity" (which was published the same day as this post) and "New Study Indicates Chimp DNA is 88% Similar to Human DNA". Further research is planned. (Of course, the seventy percent genetic similarity that we have with sea sponges often goes unmentioned.) Using assumptions, circular reasoning, and other bad arguments, resemblances are used to show that we evolved from a common ancestor. Restrain your equines, Ernie, there are some problems here.

Evolutionists point to similarities between organisms as evidence of a common ancestor. But similarities actually argue the other way.
The check's in the mail. Image credit: morgueFile / lightfoot
The hands at the Darwin Ranch are not known for their efficient reasoning abilities. Ignoring data and alternative explanations are common over there, and in this case, the possibility that similarities can be a strong indication of the Master Designer that created us all is conveniently ignored. By the way, questions of "Why?" are not in the realm of naturalism, they are theological in nature.
Evolutionists commonly argue that the supposed 98% genetic similarity between chimps and humans is evidence that they share a common ancestor. Creationists have put forward a number of responses to this, but there is an implicit assumption in both the evolutionary argument and typical creationist responses—that the higher the genetic similarity between two species, the more likely it is that they had a common ancestor. Is this necessarily the case? Might high genetic similarity, under certain circumstances, actually be evidence for design? Donald H. from the United States writes:
To see what Donald wrote and Shaun Doyle's insightful response, click on "Why did God make humans and chimps so similar?