I'm interested in minimizing ecosystem harm / impact, even if I'm not the direct / attributable source. In the worst case, if I know that an upstream hop is going to generate backscatter if I reject in my DATA phase, and I know with high confidence that the content is spam, and I know that that upstream hop is not likely to change their ways any time soon ... it's a net lessening of ecosystem harm if I silently discard, rather than indirectly "trigger" predictable backscatter.
Yes, I know this is idealistic. :D