re: what o_e_l_e_o said: I like that idea but that would massively shrink the size of DT2. I guess that's not necessarily a bad thing?
Loyce crunched some numbers on that a few months ago. At the time, it would have shrunk the list of DT2
from 229 to 63.63 was probably a bit on the low side, considering we have 100 DT1s (or usually around 95 if you exclude the handful who are excluded). However, given the DT2 list has now almost doubled at 434, if the ratios were to stay the same (I'm not saying they would, but as a ballpark) we would be looking at around 110-120 DT2 users, which I think is entirely reasonable.
I think you are far less likely to have someone who is trusted by 2 DT1s "doing something stupid" than someone who has a single inclusion, as per OP's concerns. It also gives you two users rather than one you can appeal to if they do - they only have to lose one of their inclusions to drop off of DT2.
I think that's a reasonable enough idea then. Rather than having it just apply to DT2, maybe add in an option to change the minimum number of trusts required for someone a depth below to appear on your trust list, and set the default to 2 - so by default you would trust 2 depths below your trust list, and for someone to appear a depth lower on your trust list they need to be trusted by two people a depth higher. Could be called 'trickle-down factor' or something similar.
I have less of a problem with DefaultTrust right now however than I do with trust ratings being used for disagreements and petty things. There are a few people on DT1/2 who use negative trust against people just because they spouted some opinions they didn't like, and pad their reasoning with some words about how "this makes them untrustworthy". It's very blatant mis-use of the system IMO.