I frankly don't know why it is offensive to religious people in general. However, I can certainly see how people can get worked up over it if they interpret the creation myths (in practically any religion) as literal things.
Theistic evolution is still possible. But the role of a creator, as far as I can see, is still outside the realm of falsifiable hypotheses. Most people I've met invoke God as explanation for the unexplained. Frankly, this is the "God of the Gaps" and believing in this God also runs against the scientific spirit, and more broadly, the human spirit, to ask about and find out about things.
A God of explanations is too impotent a God for my tastes, and I do believe in God.
Edit: "Intelligent design" is marginally more interesting than exploring a particular creation myth in its literal interpretation. But the more interesting the Intelligent Design process proposed, the more it resembles the process we call evolution. It would be interesting if we could somehow have a serious debate about theistic vs. atheistic evolution based on people who can actually tease out the differences in prediction based on a real understanding of probability, statistics, and information.