Because, even now, I believe there is a majority consensus among sensible people that there is a god. That means that believers have persuaded most other reasonable people that there is a god. It seems to me that anyone who goes against this common acceptance must justify his position rather than the other way round.
That's a problem for the scientists to solve, and if they can't then science is too limited to be used as a method for deciding whether gods exist. Many scientific discoveries have been the result of inferring their existence, and then establishing whether the conditions existed to allow those "theoretical" objects to be. Do the same for gods, or admit that science is inadequate for that particular purpose.
For example - and I'm not offering this as a genuine argument, but simply as an illustration - you might infer god needs to be believed in to exist. You can then argue that god does not exist in any place where there is no faith. If you find any place in the universe or multiverse where faith exists at any time, you can then begin a search to find him. Maybe you will: that will be conclusive. Maybe you won't; that will leave the question open and reveal the limitations of your approach.
Remember also, the majority of reasonable people believe in gods: few reasonable people believe in unicorns.
Yes anywhere, any time, any dimension. If we don't have the tools to prove our case, we must find them or accept the possibility of gods may be a real one and that our denial is just another act of faith. You can't blame religionists for science's shortcomings.
You are doing precisely the same: claiming that belief in gods is unscientific, when science may be entirely irrelevant to the question. To deny the existence of god is just as much an unprovable assertion as to believe in the existence of gods. The evidence for god is all around us, but you interpret that same evidence as demonstrating his absence. Clearly, the evidence, either way, is inconclusive. Evidence, therefore, is unreliable for resolving this particular problem.
Finally, Clarke is wrong, technology is not to be confused with magic. Magic, if it works at all, works without technology - possibly in spite of it.