Why does making the following statement make the speaker dumb?

Not really. Intelligence and faith in God do not have to be diametrically opposed. I prefer the following statement:

I can never prove the existence of God but I do not need proof to believe.

That is both true and empowering because you are not tacking your faith on to something that needs to be proven in the first place.

No one can 'know' anything. Knowing means it can be said without any possibility of being wrong that God exists and if you really did know, there would be no debates about God's existence.

Edit: There is a difference in saying 'God exists' and saying 'God exists for me'. The latter is subjective and subjectivity is non-debatable. Objectivity (God exists) means you're making a claim that applies to the entire world - a truth that exists for everyone. So you're speaking for everyone when you say 'God exists'

Because it implies that because the speaker has their own emotional surety that God exists others should accept that and should require no proof to believe the same. It also shows that the speaker believes without real evidence, but just a feeling. Now I have no problem with that but call it what it is. That person doesn't really "know".

faith does not equal proof, otherwise the following statement would be true:

i dont need proof that i have millions in my bank account, i know i do.

but faith fails at making that true. also incorrect grammar. like this. sentence fragments. make you look like an idiot.

and one more thing, god is not a name even the bible says so, thus you dont capitalize it unless it's at the beginning of the sentence.