Intelligent design is a modest position theologically and philosophically, which attributes the complexity and diversity of life to intelligence, but does not identify that intelligence with the God of any religious faith or philosophical system.
Intelligent design is to be rejected because design is really not all that intelligent: Over 99% of all species are extinct, and rather than optimal design, we see redundancy, regressions, and unnecessary complications... bewildering inefficiencies that result in suffering and death... species of fish, salamanders, and crustaceans that have nonfunctional eyes, because they continued to evolve in darkness for millions of years.
Intelligent design is, unlike creationism, a science in its own right and can stand on its own feet.
Intelligent design is a theory whose conclusion flows naturally from the data itself, and to infer that biochemical systems were designed by an intelligent agent requires no new principles of logic or science.
Intelligent design is not the opposite of evolution. Rather, it is the opposite of Darwinism, which says life evolved by an utterly unguided, undirected mechanism.
Intelligent design is flawed because there is absolutely nothing at all to say that even if there were a designer, that it would be the biblical God, and that it would approve of Christianity... it could just as well be running as a simulation on an alien supercomputer. Or it could be the work of an evil God, or of two such Gods playing tug-of-war with a larger cosmos.
Intelligent design is based on the flawed notion that space and time, because they exist, must be caused by something outside of space and time.
Intelligent design does not turn the study of biological origins into a Bible-science controversy, and is thus a position around which Christians of all stripes can unite.