While I don't agree with the logic, this is probabely the reason girl on girl scenes are accepted by mainstream porn while guy on guy scenes are not:

The Christian Bible, The Torah, and the Koran all forbid male on male sexual contact and the price of such contact is death.

Nowhere in any of these books is girl on girl sexual contact forbidden.

So, according to the inerrant, verbatim word of God, lebianism is not a sin. Male homosexuality is a sin punishable by death and eternal damnation.

Nuf Said.
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I'd rather be ignorant than stupid. Ignorance implies a lack of knowledge which is easily correctable through education. Stupidity implies an inability to learn. Therefore; ignorance is temporary, stupidity is forever!