An argument against God

[John V]

(1)If God exists, it would be a favor if humanity knew he existed beyond doubt.

Not necessarily true. Depends on the god. For a deist god, what difference would it make?

Regarding Christianity, James says that the demons believe in God - and shudder. Plenty of atheists say that they wouldn't worship God even if convinced of his existence. So this doesn't apply to the God of the Bible.

(2) God can prove his existence beyond doubt.

Some atheists would argue against this, but I'm with you on this one. I believe God will eventually prove his existence beyond a doubt.

(3) God being all benevolent

This should be its own point. you've really limited the application of the argument with this one. For example, it doesn't apply to the God of the Bible, as things like the flood or the plagues don't seem benevolent.

would want to be bestow the favor of being knowing beyond doubt by all of humanity.

Since this follows from 1 and 1 isn't generally applicable, neither is this point. It might be applicable for some gods.

(4) He is not known beyond doubt by all of humanity.

OK.

(5) Therefore God doesn't exist.

Since 1, 3a and 3b are very restricted in applicability, so is the conclusion. I suppose you've ruled out gods who are all benevolent and for whom knowledge of the god is beneficial to humankind. Is there a particular god you had in mind? It doesn't fit any that are coming to my mind.