Superman as a Christ allegory? Very likely. It has enough of the aspects of the Christ story to be plausible.
Superman gay? Not even plausible, and not worth mentioning. Must be wishful thinking on the part of homosexuals. I know I've found myself thinking that a hot lesbian was a terrible waste. I'm sure homosexuals feel the same way about heterosexual hunks with a reputation for endurance, control, and a penchant for tights.
Superman Jewish? Good old, corn fed Kansas beef... Superman is not likely to be Jewish, although his creators may have injected some of their life experiences into his character. His moral certainty, and decisive actions are probably a projection intended to resonate with the American public at large, thus encouraging an America that is willing to act against evil wherever it may occur. The end result is an America willing and able to defend the innocent, including Jews. Admittedly, somewhat cynical - but I didn't ask the question.
See the part that really gets liberals down is Superman's motto:
'Truth,Justice and the AMERICAN way'
Just can't have that in the U.S. It excludes the non-supermen.
"Superman stands alone. Superman did not become Superman, Superman was born Superman. When Superman wakes up in the morning, he is Superman. His alter ego is Clark Kent. His outfit with the big red S is the blanket he was wrapped in as a baby when the Kents found him. Those are his clothes. What Kent wears, the glasses the business suit, that's the costume. That's the costume Superman wears to blend in with us. Clark Kent is how Superman views us. And what are the characteristics of Clark Kent? He's weak, unsure of himself... he's a coward. Clark Kent is Superman's critique on the whole human race..."