Why would allowing marriage de-incentivize a gay person from entering the priesthood? As for being openly gay, I don't think the church has any rule against that (not any more than being openly hetero at least). #3 seems pointless unless you believe that being gay makes one more likely to prey on children.
I'm not trying to be difficult, I just cannot reconcile the argument that a "link" or "correlation" is important to recognize without also presuming that gays are more likely to be child molesters.