"If one believes in ID, the next step he will ask is the purpose of creating life. This will ultimately lead back to religion."
Not necessarily.
Just as it is the nature of living beings to be born, to live, and then to die...to attempt to survive and procreate...these aspects of their nature are not a function of a willful decision or acting for a purpose but rather they are just following their instinctive programming, following their own nature.
We wouldn't say that the purpose of a single celled organism is to survive, we would say that it is the nature of the organism to survive.
We would say the single celled organism exists, lives, but we would not be able to state a purpose for that single cell organism to necessarily exit.
That's because the single celled organism is just a piece of the totality of the Universe. Science doesn't examine the purpose of the parts of the Universe, they examine the functionality of the parts. They have no way of knowing if the Universe as a whole has purpose or meaning beyond its own existence as a totality.
Just like a car has lots of parts that function with no sense of purpose or duty, the parts in the drive train don't function as a result of their own intended purpose. It is we who project purpose onto those parts as they serve the larger purposes we establish, which is ultimately transportation. We need to go where we are not.
Purpose has to do with intent, it has to do with the mind having goals beyond simple biological function. This is the difference between the nature of something and its purpose. Purpose serves something that is not intrinsic to the part.
Could a designer of the Universe have no purpose?
Yes, of course. A designer of the Universe could simply have a
nature to design, and no intention to design for a larger purpose.
So a designer of the Universe could design the Universe by virtue of their own nature of being a designer without having any purpose in doing so. Their motivation would not be to fulfill a purpose. They are just following their nature, not acting out of some external purpose to their own nature.
Quote from yip1997:
I don't really know the true definition of creationism. Please correct me if i am wrong.
Going back to OP, it seems to me that ID is a superset of "creationism". IOW, intelligent design = create on purpose.
Life can be created by laws of nature (such as evolution, mutation etc) without the intent of creating life. Creationism just means there is an origin or the beginning of life.
If one believes in ID, the next step he will ask is the purpose of creating life. This will ultimately lead back to religion. 
