It doesn't sound familiar because nobody here is saying God is impossible. We're saying they don't have good reason for believing he exists.

I don’t go around telling ten-dimensional physicists to stop believing in, and speculating about, a theoretical field that’s devoid of evidence.

You wouldn't have to tell them to stop "believing" in string theory because none of them do. The math happens to work out so a lot of them are interested, but none of them "believe" in it because it hasn't been tested.

Why are the atheists in this thread qualified to tell them they are wrong to hold it?

We're not saying they're wrong. We're saying their reasons for believing aren't good reasons. And in a thread about why people believe, criticism is not only warranted, but expected.

Gnostic atheists were imposing their own beliefs on the religious through unsolicited critical condemnation.

Can you point me to even one atheist here making a gnostic claim? The link you already gave is just Communist saying you don't have evidence, and it seems like you're translating every other instance of that to "GOD ISN'T REAL".