Exactly, if God's existence is "proven", then who would reject him? Everyone, regardless of their goodness, would want to be on the side of the omnipotent all powerful being.
It takes no effort to have faith to a God that know is there, and ultimately that why we're here. This place, here and now, is the real test faith, if you can keep your faith even here, without being able to materially sense him, only then do you confirm your faith to be real.
That's why it's so funny that people say "if god exist why doesn't he just show himself and prove it, then I'd believe in him." God is not being tested, we are, and God isn't about the bail us not by answering the question for us.
Elijah proved God rather conclusively with the prophets of baal.
But I don't recall all those on the other side immediately converting.
Stubborn rebellion is it's own arrogant god.
GREAT POINT.