Go to the entrance of the church dressed like a homeless person and ask for help, then see what they do about it.
If they respond correctly and indeed help you, go to the street and pick up as many homeless people as you can and send them their way, not all at once, just a few today, and repeat tomorrow.
This way they will be doing something good, to counter the something bad that's about to be done.
Flaming them will not help, kicking them out will not help either... I guess they are what you'd call a "resolved people", they choose that belief because of your resistance and they are actually counting on you and everyone else to be against them, don't ask me why is that

Edit note: I'm not familiar with westboro church, such a thing does not exist round here, I'm just basically applying people relations knowledge to this.