Well, since TS requested for my opinion on this subject I am happy to oblige.
There are many ways to spread the message of "good", as there are many ways to spread the message of "evil". Metal has always been associated with "evil", cos it sounds angry, loud and destructive, so that stigma is something that is basically hard to get rid of. On the contrary, Faith itself is seen as something associated with "good" cos it suppose to promote calm, peace and constructiveness.
I understand the TS's point of view. That paradox seems to contradict each other; faith and religion is sacred. To have it associated to anything that is remotely "evil" is wrong, sacrilegious and taboo.
But doesn't God (if you believe in Him/Her) have an angry, loud and destructive side too? We see don't see it as a negativity, rather as a necessity. So if such aggression can be seen as a necessity, I do not think there is anything wrong in spreading the faith by embracing the natural aspect and facet that exist in all. Perhaps it is a necessity cos it speaks more to the people who can ASSOCIATE to that kind of sound.
What should be your concern instead, is not HOW the message is conveyed, but WHAT message is conveyed. A good example is how the JI movement established itself. Was the message of hate spread via Islamic metal songs that speaks highly of teh faith? No. It is spread through simple discussions and communications via context and situations that is seen as "holy" and "religious".