I'm not sure that it is a matter of belief.
Yes, I agree that IF is just one scientometric index that states nothing about the quality of the journal nor the quality of the paper published in that journal. Yes, it shouldn't be so important. Unfortunately, it became the second most important thing among researchers, and many Scientific agencies rank their scientists by it as well as give funding.
In short, I don't believe in it. At the same time, I don't believe in Santa either. But I will not mind receiving a gift from him from time to time.