People on this site love to espouse that children should be encouraged in their sexuality, blah blah blah, but when someone comes along and says he is befriending (or fantasizing about befriending) a little girl for the purpose of gaining her trust so they can open her up to her sexuality, everybody freaks out.

Why? The two sides of your equation are not equal.

The purposes of "grooming" are manifold. If, for example, you are "grooming" a future adult in an effort to supplement the (lack of) information (s)he is receiving elsewhere, for the sole purpose of helping that person become an educated individual, then this is beneficial to all involved (save those with a "moral", financial, or other stake in their you-learn-only-what-we-want-you-to-know system of "education").

The post you reference, however, was a virtual admission that the sole purpose for his "grooming" would be to gain himself a future sex partner.

Apples v. oranges.