So if a scammer made it onto default trust (it is inevitable in a decentralized system rife with scammers), would excluding everyone that included that scammer remove the scammer from default trust?
No, exclusion of voter will not effect on DT1 network. If scammer become DT1 by voting system and he trusted by 5 DT1 but if you want to remove him from DT network then 6 DT1 should be exclude him. Its same for DT2 as well.
For example you are trusted by 31 DT1 members. If someone like to exclude you from DT network then 32 DT1 have to exclude you.
Exclusion of DT2 and other members will not effect on remove from DT network.