Science is the body of knowledge developed by the application of the scientific method, which is basically the formulation of hypotheses, the development of tests that could falsify those hypotheses, the gathering of data from those tests, the reaching of the minimal conclusion that data can support, and the sharing of all of that work with the community of all the other people who are following the same process (and others, too), with the aim that they will look over your shoulder and catch any mistakes you might have made.
When we say that ID is not science, it's because there's absolutely no indication they've been able to do any of those steps. They don't start from data; they start by picking the conclusion and rejecting what doesn't fit. They don't start with a hypothesis that they consider how to disprove; they start with by making up whatever dishonest arguments they can think of. They don't publish their data, methods, and results for the sceptical scientific community to pick over; they publish in books they know scientists won't read, targeting those who don't have the training to see through their deception.
They just don't do science. It's all politics, for them.
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