Slander doesn't just wipe off, even if you theoretically win a lawsuit. It's still "there", which is why it's such an insidious mortal sin. It violates the commandment, "Thou Shalt Not Murder".
So, how many innocent priests are you willing to sacrifice to drive out the homosexuals? I don't disagree with keeping them out of the priesthood, I do disagree strongly with this "expedient" method that will undoubtedly harm the innocent.
And yes, the Church has everything to lose: every good priest that fears they will be the next innocent victim of vicious slander will suffer, and every good candidate for the priesthood will rightfully rethink their decision if it becomes apparent the Church will not defend their own.