Three things occur to me: 1: I think there is a reason for a cutoff. To take the AI case: I have no doubt that any AI worth its salt could suffer. But that AI will (probably) be build from transistors and I think that it is meaningless to consider the suffering of a thermostat. So there's a cutoff somewhere - maybe it isn't that 'hard' but some things are on one side and some on the other. Flies, I think, are more like thermostats and I value each one of them at very close to zero. But you are right, possibly not >exactly< zero and that eps might add up in some way. Would destroying a billion thermostats be ethically problematic?

2: Scott Alexander has written on this recently and it covers much of the same ground that we are covering here: https://astralcodexten.substack.com/p/i-will-not-eat-the-bug...

3: Some time ago I seem to remember the Swiss Government discussing a proposition to recognise the 'dignity' of insect and plants. Dignity was held to be a property distinct from suffering and I think part of the argument was that it was somehow mutual: damaging life in any form was harmful to the dignity of both the damager and the damagee. I have some sympathy with that idea. In other words, we should care about the bugs because we care about ourselves.

Disclosure, I do a lot of scientific work with Drosophila and this is something that I mull over from time to time as I slaughter them in their thousands...