Okay, so...since a penis was involved in the creation of just about everyone in one way or another, certainly we can't be offended by the word penis. Granted, the above statement does mention whipping it out in public and waving it around, but it's prefaced by the words please don't. So that's okay, right?
Hmmm... PLEASE don't try to shove it down my children's throats. Well, yes, okay... that's some pretty evocative imagery, true. But again, it's saying PLEASE don't.
Maybe it's the comparison of religion to a penis. But then that only works if you attach negative connotations to the idea of a penis. Not me. I happen to have a certain fondness for them. The idea of a penis evokes acts of pleasure, acts of love, and acts of creation. I think the world would be a sad place without penises.
I also happen to have a certain fondness for religion. All of them. Spirituality in general fascinates me. I know God, and I even think Jesus was a pretty cool guy. But...