When you are making a house do you build the foundation first or go start on the attic?
Believe a BG and there is little risk of being led astray day one. It also gives us a vote pattern to use as something to base the seer believe from. It also doubles the number of potential blocks for tonight which puts more pressure on the wolves.
Worst case scenario we believe a wolf as the BG and just don't get the extra block but we have in effect lost NOTHING.
A second BG is huge but everyone is not only being led down a road to the seer believe but by the person who has suggested it. You are saying the only risk is if the cunning gets the seer role but that is not true at all. It is a risk not only if any one the wolves get the role but it the cultist gets that role it is just as deadly, if not even more so.