It's Simple: Only Science in the Science Classroom
Some Darwinists have sometimes argued that if ID were taught in schools, then that would risk opening the science classroom to a floodgate of religious ideas about origins, wreaking havoc upon the classroom and turning it into a platform for religious proseltyzation. (For an older example of this objection, see Robert Pennock's Tower of Babel, pg. xviii.) David Brin repeats this red herring in "The Other Intelligent Design Theories: Intelligent Design is only one of many 'alternatives' to Darwinian evolution," which is the cover story of the current Skeptic Magazine. Brin suggests that if ID is taught, the science classroom will be opened to an onslaught of other "'alternatives' to Darwinian evolution" (which he thinks would might offend the sensibilities of the average ID proponent, whom he unskeptically assumes are all orthodox Christians).
Here's a one-sentence response to Mr. Brin's article and the large number of other critics who claim that teaching ID would open the door to a flood of other "creation theories," thus wasting time and student understanding of science:
Only science belongs in the science classroom, and most of the non-ID "alternative[s] to Darwinian evolution" described by Mr. Brin in his parade of horribles (i.e. "Guided Evolution," "Intelligent Design of Intelligent Designers," "Cycles of Creation") are clearly religious alternatives, so there's no reason to suspect that teaching the scientific theory of ID would invite a flood of those non-scientific religious viewpoints into the science classroom.
It's really uncomplicated: Evolution is science; it can be taught in the science classroom. Theories of self-organization are science; they can be taught in the science classroom. Intelligent design is science; it could be taught in the science classroom. And if panspermia and Lee Smolin's theory of reproducing universe can be formulated in scientific terms (which they probably can), then they too can be taught in the science classroom. But religious doctrines involving Vishnu, the Deity of Mormonism, or God-Guided Evolution are not science, but religion, and cannot be taught in a science classroom. The objection that teaching the scientific theory of ID will lead to an "invasion of creation theories," many of which are religious, is false.