Just to clarify, what are the current blocks that players are allowed to grief/steal during a raid?
I would like to point out that the more blocks that are added to the list as "steal-able" during sieges (I am assuming that is what Beau_Nearh means by steal/grief during raids) the fewer blocks people will use in their buildings.
I love to build myself, so I hate to keep adding more and more blocks to what may be stolen from builds. Perhaps I can see allowing Diamond, Gold, and Emerald blocks to be stolen (though I'm not even fond of this), but I don't think Iron, Coal, Redstone, or Lapis should be allowed to be stolen/griefed from builds. They are not rare enough to merit this. Also, as I have mentioned, this would mostly eliminate these blocks from being used in building.
Furthermore, if what Beau_Nearh means is to add them to the list of "soft-blocks" of siege, this doesn't make sense for Iron and Diamond blocks especially. They are the toughest materials in game.
I would caution adding so many blocks to the steal-able/grief-able list. Bookshelves would simply break without silk touch correct? And Brewing Stands can only be removed by Alchemists right? Same goes for Engineer's and respective items. I can't remember if these can be broken or not.
If heads can be stolen people will never display them as trophies, but will simply hide them away in chests. What is the fun in that?
A lot of what I am suggesting is that if you add the blocks as items that can be stolen from builds, then you are reducing them to items of monetary value and stripping them of their worth as building/decorative blocks. I don't want this.