Fungibility matters if your only goal is to make it impossible for bad dudes to sell their product / invest. But keeping your own hands clean is an admirable goal in and of itself, and certainly concluding "this doesn't make a difference in the grand scheme so why should I care" seems to be the exact kind of cynicism the parent comment was critiquing
The point is that some things make a proportional difference, which at the level of an individual is minimal but make a real impact if 30-70% of people do it, whereas other things only work with a critical mass, which are then still useless even if 30-70% of people do them because you need 70-100% of people to do it for it to be effective at all.
If you as an individual are going to do something, do the first kind of thing.
